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单选题
If the earth suddenly ________spinning, people would all fly off it.
A
had stopped
B
stopped
C
has stopped
D
would stop
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解析：
更多 “单选题If the earth suddenly ________spinning, people would all fly off it.A had stoppedB stoppedC has stoppedD would stop” 相关考题
考题
If all the people in the world spoke the same language, cultural and economic ties_________ be much closer among countries now.A． willB． shouldC．shallD． would
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BHave you ever wondered?1.Why do airplanes take longer to fly west than east?It can take five hours to go west-east from New York(NY) to London but seven hours to travel east-west from London to NY. The reason for the difference is an atmospheric phenomenon know as the jet(喷射) stream. The jet stream is a very high altitude wind which always blows from the west to the east across the Atlantic. The planes movement a constams air speed thus go faster in the west-east direction when the air moving with the wind than in the opposite direction.2 What would happen if the gravity on Earth was suddenly turned off?Supposing we could magically turn off gravity. Would buildings and other structures float away? What happened would depend on how strongly the things were attached to the Earth. The Earth is moving at quite a speed moving at over a thousand miles per hour. If you turn something round your head on a string, it goes around in a circle until you let go of the strong go of the string. Things not attacked to the Earth would fly off in a straight line . People in buildings would suddenly shoot upwards at a great speed until they hit the ceiling. Most things would fly off into space.60.What information coa we get from the first passage?A.tis the iet stoomn that affeets how fast airplanes fly.B.Planes go slower when they are moving with the wind.C.It takes more time to fly from NY to London than from London to NY.D.The jet stream always blows from the east to the west across the Atantic.
考题
It can be interred that without gravity .A.buildings and other structures would float awayB.trees and buildings would not so easily fly offC.something around your head would not float awayD.everything outside buildings would fly off into space
考题
Text 2 To understand how astrology works, we should first take a quick look at the sky. Although the stars are at enormous distances, they do indeed give the impression of being affixed to the inner surface of a great hollow sphere surrounding the earth. Ancient people, in fact, literally believed in the existence of such a celestial sphere. As the earth spins on its axis, the celestial sphere appears to turn about us each day, pivoting at points on a line with the earth's axis of rotation. This daily turning of the sphere carries the stars around the sky, causing most of them to rise and set, but they, and constellations they define, maintains fixed patterns on the sphere, just as the continent of Australian maintains its shape on a spinning globe of the earth. Thus the stars were called fixed stars.The motion of the sun along the ecliptic is, of course, merely a reflection of the revolution of the earth around the sun, but the ancients believed the earth was fixed and the sun had an independent motion of its own, eastward among the stars. The glare of sunlight hides the stars in daytime, but the ancients were aware that the stars were up there even at night, and the slow eastward motion of the sun around the sky, at the rate of about thirty degrees each month, caused different stars to be visible at night at different times of the year.The moon, revolving around the earth each month, also has an independent motion in the sky. The moon, however, changes its position relatively rapidly. Although it appears to rise and set each day, as does nearly everything else in the sky, we can see the moon changing position during as short an interval as an hour or so. The moon's path around the earth lies nearly in the same plane as the earth's path around the sun, so the moon is never seen very far from the ecliptic in the sky. There are five other objects visible to the naked eye that also appear to move in respect to the fixed background of stars on the celestial sphere. These are the planets Mercury, Venus, Mars, Jupiter, and the Saturn. All of them revolve around the sun in nearly the same plane as the earth does, so they, like the moon, always appear near the ecliptic. Because we see the planets from the moving earth, however, they behave in a complicated way, with their apparent motions on the celestial sphere reflection both their own independent motions around the sun and our motion as well.第26题：The ancient people believed that ________.[A] the earth was spinning on the axis of the sky[B] the sky was a hollow sphere spinning around the earth[C] the patterns of stars on the sky would never change[D] the stars around the sky were not stationary
考题
According to the passage which of the following is true?[A] A fixed star refers a star that is always stationary on the sky.[B] Scientists can tell the motion of the earth from the motions of other five planets.[C] Ancient people had scanty knowledge about the movement of the stars.[D] All the stars on the sky can be seen all the year around.
考题
______ a little more tolerant our world would be a better place.A. Were peopleB. If people wouldC. People wereD. Would people
考题
The officer allowed ______.A. the students to fly the plane all the timeB. all students to fly the planeC. the students who were not frightened to fly on their ownD. some students to fly a little while
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"I ask you to drink to his health as a young man full of the spirit of adventure who has lit up the world with a flash of courage. "With these words, the British Minister of Air turned and raised his glass to the young man who sat beside him-a young man who, only a month before, was completely unknown. Yet on that summer day in 1927 his name was on the world's lips-Charles Lindbergh, the first man to fly the Atlantic alone.He had been an air mail pilot, flying back and forth between Chicago and the city of St. Louis. Determined to win the $5, 000 prize offered by a fellow American for the first flight form. New York to Paris, Lindbergh had persuaded a group of St. Louis businessmen to finance the building of a special plane for him.The news that Lindbergh intended to fly the Atlantic alone was received with disbelief. The plane would never fly, people said. It would run out of fuel. It had only a single engine. Lloyds of London refused to insure the flight. Men called Lindbergh the "flying fool".But on May 20th, 1927, just after ten to eight in the morning, Lindbergh's "Spirit of St. Louis", heavily laden with fuel, struggled into the air from a New York airfield. For several hours the weight of the petrol prevented the young pilot from flying more than a few feet above the wave-tops. Night came and thick fog covered up the stars. Lindbergh flew steadily on, hoping that his course was the right one. He struggled to keep awake, checking the fuel all the time to keep his mind active. Throughout the next day the "Spirit of St. Louis" flew on over the seemingly limitless sea. Then a fishing boat appeared, and, an hour later, land. It was Ireland. Lindbergh set a compass course for Paris.By ten o'clock the lights of France's capital were shining beneath him. Tired, unshaved, suddenly hungry, the "flying fool" came down to Le Bourget airport, and landed in front of a huge crowd of wildly cheering people. After 34 hours of continuous piloting, the flight of 3, 600 miles was over.1. The British Minister of Air _____.A. praised Lindbergh for his intelligenceB. encouraged Lindbergh to be more adventurousC. congratulated Lindbergh for his braveryD. warned Lindbergh not to fly alone2. "… his name was on the world's lips"means _____.A. "Everybody was drinking to his health"B. "Everybody was jumping about because of him"C. "He became suddenly unpopular"D. "Everybody was talking about him"3. A group of St. Louis businessmen had been persuaded to _____ the building of a special plane.A. arrangeB. organizeC. stopD. pay for4. Which of the following is true? _____A. Nobody at all believed that it was foolish for anybody to try to fly the Atlantic.B. Everybody knew that Lindbergh was very brave and adventurous.C. People didn't believe that Lindbergh really meant to fly the Atlantic alone.D. Everybody believed that it was foolish for anybody to try to fly the Atlantic at all.5. The "Spirit of St. Louis" here refers to _____.A. the plane Lindbergh flew inB. the"flying fool"C. the hope of the people of St. LouisD. the city of St. Louis
考题
A place is moved from day into night and from night into day over and over by ______ of the earth.A.the pushing B.the pulling C.the spinning D.the passing
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第二篇Human and the EarthIn terms of the evolution of life on Earth,human beings have just arrived.Despite their shori time on Earth,however,people have brought about enormous changes to the surface of the planet一changes far out of proportion to the interval of time they have occupied it.People have more control over their surroundings than any other species on Earth.With the combination of intelligence and manual skill(allowing us to make and use tools),people have found ways to use plant and animal resources,mineral ores,fuels,and many other materials and resources from the Earth.As the number of people on Earth increases,it becomes increasingly difficult for the population to survive on the resources of the land.The amount of land is limited.Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer,the land ultimately can produce only so much food and no more.As the human population grows,people consume more.Clearly,some locations on Earth already have too many people;in many of these areas,future increases will surely bring about more poverty and suffering. Yet people in rich nations use proportionally far more of the available resources than people in poorer nations.As they consume these resources without restraint,they also waste large amounts of them.People are only a very small fraction of all the living things on the planet.Yet their numbers create a drain on resources that can't be renewed.For example,the amount of water on Earth is limited,this water is cleaned through natural processes.However,the natural processes for filtering water can clean only a certain amount of water by removing the pollution.Likewise,a limited amount of petroleum can be found under the Earth's surface.Petroleum is a valuable resource.Should people use it up to manufacture petrol for automobiles?As people work to control the planet and make life comfortable,are they using up resources that are needed for their survival?Why have people more control over their surroundings than any other species on Earth?A:Because of their intelligence and manual skill.B:Because they can use plant and animal resources,mineral ores and fuels.C:Because they are cleverer than any other animals on Earth.D:Both A and B.
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Who Want to Live Forever?If your doctor could give you a drug that would let you live a healthy life for twice as long,would you take it?The good news is that we may be drawing near to that date.Scientists have already extended the lives of flies,worms and mice in laboratories.Many now think that using genetic treatments we will soon be able to extend human life to at least 140 years.This seems a great idea.Think of how much more time we could spend chasing our dreams,spending time with our loved ones,watching our families grow and have families of their own."Longer life would give us a chance to recover from our mistakes and promote long term thinking," says Dr.Gregory Stock of the University of California School of Public Health."It would also raise productivity by adding to the year we can work."Longer lives don't just affect the people who live them.They also affect society as a whole."We have war,poverty,all sorts of issues around,and I don't think any of them would be at all helped by having people live longer,"says US bioethicist Daniel Callahan."The question is‘What will we get as a society?'I suspect it won't be a better society."It would certainly be a very different society.People are already finding it more difficult to stay married.Divorce rates are rising.What would happen to marriage in a society where people lived for 140 years?And what would happen to family life if 9 or 10 generations of the same family were all alive at the same time? Research into ageing may enable women to remain fertile for longer.And that raises the prospect of having 100-year-old parents,or brothers and sisters born 50 years apart.We think of an elder sibling as someone who can protect us and offer help and advice.That would be hard to do if that sibling came from a completely different generation.Working life would also be affected,especially if the retirement age was lifted.More people would stay in work for longer.That would give us the benefits of age-skill,wisdom and good judgment.On the other hand,more people working for longer would create greater competition for jobs.It would make it more difficult for younger people to find a job.Top posts would be dominated by the same few individuals,making career progress more difficult.And how easily would a 25 -year-old employee be able to communicate with a 1 25 -year-old boss?Young people would be a smaller part of a society in which people lived to 140.It may be that such a society would place less importance on guiding and educating young people,and more on making life comfortable for the old.And society would feel very different if more of its members were older.There would be more wisdom, but less energy.Young people like to move about.Old people like to sit still.Young people tend to act without thinking.Old people tend to think without acting.Young people are curious and like to cxperience different things.Old people are less enthusiastic about change.In fact,they are less,enthusiastic about everything.The effect of anti一ageing technology is deeper than we might think.But as the science advances,we need to think about these changes now."If this could ever happen,then we'd better ask what kind of society we want to get,"says Daniel Callahan."We had better not go anywhere near it until we have figure those problems out." All of the following are possible effects living longer might have on working life EXCEPT______.A:communication between employers and employees would be more difficultB:more money would be used by employers in payment of their employeesC:the job market would be more competitiveD:it would be more difficult for young people to be promoted to top positions
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第二篇Human and the EarthIn terms of the evolution of life on Earth,human beings have just arrived.Despite their shori time on Earth,however,people have brought about enormous changes to the surface of the planet一changes far out of proportion to the interval of time they have occupied it.People have more control over their surroundings than any other species on Earth.With the combination of intelligence and manual skill(allowing us to make and use tools),people have found ways to use plant and animal resources,mineral ores,fuels,and many other materials and resources from the Earth.As the number of people on Earth increases,it becomes increasingly difficult for the population to survive on the resources of the land.The amount of land is limited.Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer,the land ultimately can produce only so much food and no more.As the human population grows,people consume more.Clearly,some locations on Earth already have too many people;in many of these areas,future increases will surely bring about more poverty and suffering. Yet people in rich nations use proportionally far more of the available resources than people in poorer nations.As they consume these resources without restraint,they also waste large amounts of them.People are only a very small fraction of all the living things on the planet.Yet their numbers create a drain on resources that can't be renewed.For example,the amount of water on Earth is limited,this water is cleaned through natural processes.However,the natural processes for filtering water can clean only a certain amount of water by removing the pollution.Likewise,a limited amount of petroleum can be found under the Earth's surface.Petroleum is a valuable resource.Should people use it up to manufacture petrol for automobiles?As people work to control the planet and make life comfortable,are they using up resources that are needed for their survival?in terms of the evolution of life on Earth,the history of human beings is_______.A:very short B:very longC:as long as that of other animals D:as long as that of the Earth
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第二篇Human and the EarthIn terms of the evolution of life on Earth,human beings have just arrived.Despite their shori time on Earth,however,people have brought about enormous changes to the surface of the planet一changes far out of proportion to the interval of time they have occupied it.People have more control over their surroundings than any other species on Earth.With the combination of intelligence and manual skill(allowing us to make and use tools),people have found ways to use plant and animal resources,mineral ores,fuels,and many other materials and resources from the Earth.As the number of people on Earth increases,it becomes increasingly difficult for the population to survive on the resources of the land.The amount of land is limited.Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer,the land ultimately can produce only so much food and no more.As the human population grows,people consume more.Clearly,some locations on Earth already have too many people;in many of these areas,future increases will surely bring about more poverty and suffering. Yet people in rich nations use proportionally far more of the available resources than people in poorer nations.As they consume these resources without restraint,they also waste large amounts of them.People are only a very small fraction of all the living things on the planet.Yet their numbers create a drain on resources that can't be renewed.For example,the amount of water on Earth is limited,this water is cleaned through natural processes.However,the natural processes for filtering water can clean only a certain amount of water by removing the pollution.Likewise,a limited amount of petroleum can be found under the Earth's surface.Petroleum is a valuable resource.Should people use it up to manufacture petrol for automobiles?As people work to control the planet and make life comfortable,are they using up resources that are needed for their survival?Which of the following statements about resources on Earth is not correct?A:They can not be renewed.B:Water is a kind of resource which can not be renewed.C:Some of the resources are valuable.D:Many resources can be recycled so we don't need to worry about them.
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第二篇Human and the EarthIn terms of the evolution of life on Earth,human beings have just arrived.Despite their shori time on Earth,however,people have brought about enormous changes to the surface of the planet一changes far out of proportion to the interval of time they have occupied it.People have more control over their surroundings than any other species on Earth.With the combination of intelligence and manual skill(allowing us to make and use tools),people have found ways to use plant and animal resources,mineral ores,fuels,and many other materials and resources from the Earth.As the number of people on Earth increases,it becomes increasingly difficult for the population to survive on the resources of the land.The amount of land is limited.Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer,the land ultimately can produce only so much food and no more.As the human population grows,people consume more.Clearly,some locations on Earth already have too many people;in many of these areas,future increases will surely bring about more poverty and suffering. Yet people in rich nations use proportionally far more of the available resources than people in poorer nations.As they consume these resources without restraint,they also waste large amounts of them.People are only a very small fraction of all the living things on the planet.Yet their numbers create a drain on resources that can't be renewed.For example,the amount of water on Earth is limited,this water is cleaned through natural processes.However,the natural processes for filtering water can clean only a certain amount of water by removing the pollution.Likewise,a limited amount of petroleum can be found under the Earth's surface.Petroleum is a valuable resource.Should people use it up to manufacture petrol for automobiles?As people work to control the planet and make life comfortable,are they using up resources that are needed for their survival?What makes people feel hard to live on Earth?A:Fertilizer. B:Lse of machinery.C:Limited land. D:Limited mineral resources.
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第二篇Human and the EarthIn terms of the evolution of life on Earth,human beings have just arrived.Despite their shori time on Earth,however,people have brought about enormous changes to the surface of the planet一changes far out of proportion to the interval of time they have occupied it.People have more control over their surroundings than any other species on Earth.With the combination of intelligence and manual skill(allowing us to make and use tools),people have found ways to use plant and animal resources,mineral ores,fuels,and many other materials and resources from the Earth.As the number of people on Earth increases,it becomes increasingly difficult for the population to survive on the resources of the land.The amount of land is limited.Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer,the land ultimately can produce only so much food and no more.As the human population grows,people consume more.Clearly,some locations on Earth already have too many people;in many of these areas,future increases will surely bring about more poverty and suffering. Yet people in rich nations use proportionally far more of the available resources than people in poorer nations.As they consume these resources without restraint,they also waste large amounts of them.People are only a very small fraction of all the living things on the planet.Yet their numbers create a drain on resources that can't be renewed.For example,the amount of water on Earth is limited,this water is cleaned through natural processes.However,the natural processes for filtering water can clean only a certain amount of water by removing the pollution.Likewise,a limited amount of petroleum can be found under the Earth's surface.Petroleum is a valuable resource.Should people use it up to manufacture petrol for automobiles?As people work to control the planet and make life comfortable,are they using up resources that are needed for their survival?Who use more available resources according to the passage?A:Rich people on Earth. B:Poor people on Earth.C:People in developed countries. D:People in developing countries.
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Rockets in the SkyIf someone asked you,"What color is the sky?"I expect that you would answer,"Blue."I am afraid that you would be wrong.The sky has no color.When we see blue,we are looking at blue sunlight.The sunlight is shining on little bits of dust in the air.We know that there is air all around the world.We could not breathe without air.Airplanes could not fly without air.They need air to lift their wings.Airplanes cannot fly very high because as they go higher the air gets thinner.If we go far enough away from the earth,we find there is no air.What is the sky?The sky is space.In this space there is nothing except the sun,the moon and all the stars. Scientists have always wanted to know more about the other worlds in the space.They have looked at them through telescopes and in this way they have found out a great deal.The moon is about 384 ,000 kilometers away from the earth.An airplane cann't fly to the moon but there is a thing that can fly even when there is no air. This is rocket.I am sure that you are asking,"How does a rocket fly?"If you want to know,get a balloon and then blow it up until it is quite big.Do not tie up the neck of the balloon.Let go!The balloon will fly off through the air very quickly.The air inside the balloon tries to get out.It rushes out through the neck of the balloon and this pushes the balloon through the air.It does not need wings like an airplane.This is how a rocket works.It is not made of rubber（橡胶）like a balloon,of course.It is made of metal. The metal must not be heavy but it must be very strong.There is gas inside the rocket which is made very hot. When it rushes out of the end of the rocket,the rocket is pushed up into the air.Rockets can fly far out into space.Rockets with men inside them have already reached the moon.Several rockets,without men inside them,have been sent to other worlds much farther away.One day rockets may be able to go anywhere in the space.When an airplane flies too high,______.A:the air will be too thin to support its wingsB:the air will become thickerC:the air will exert pressure on itD:the air will disappear in no time
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Rockets in the SkyIf someone asked you,"What color is the sky?"I expect that you would answer,"Blue."I am afraid that you would be wrong.The sky has no color.When we see blue,we are looking at blue sunlight.The sunlight is shining on little bits of dust in the air.We know that there is air all around the world.We could not breathe without air.Airplanes could not fly without air.They need air to lift their wings.Airplanes cannot fly very high because as they go higher the air gets thinner.If we go far enough away from the earth,we find there is no air.What is the sky?The sky is space.In this space there is nothing except the sun,the moon and all the stars. Scientists have always wanted to know more about the other worlds in the space.They have looked at them through telescopes and in this way they have found out a great deal.The moon is about 384 ,000 kilometers away from the earth.An airplane cann't fly to the moon but there is a thing that can fly even when there is no air. This is rocket.I am sure that you are asking,"How does a rocket fly?"If you want to know,get a balloon and then blow it up until it is quite big.Do not tie up the neck of the balloon.Let go!The balloon will fly off through the air very quickly.The air inside the balloon tries to get out.It rushes out through the neck of the balloon and this pushes the balloon through the air.It does not need wings like an airplane.This is how a rocket works.It is not made of rubber（橡胶）like a balloon,of course.It is made of metal. The metal must not be heavy but it must be very strong.There is gas inside the rocket which is made very hot. When it rushes out of the end of the rocket,the rocket is pushed up into the air.Rockets can fly far out into space.Rockets with men inside them have already reached the moon.Several rockets,without men inside them,have been sent to other worlds much farther away.One day rockets may be able to go anywhere in the space.Which of the following statements about a rocket is NOT true?A:It can fly when there is no air.B:It can fly without wings.C:It is made of strong metal.D:It is propelled by burning gas inside it.
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Rockets in the SkyIf someone asked you,"What color is the sky?"I expect that you would answer,"Blue."I am afraid that you would be wrong.The sky has no color.When we see blue,we are looking at blue sunlight.The sunlight is shining on little bits of dust in the air.We know that there is air all around the world.We could not breathe without air.Airplanes could not fly without air.They need air to lift their wings.Airplanes cannot fly very high because as they go higher the air gets thinner.If we go far enough away from the earth,we find there is no air.What is the sky?The sky is space.In this space there is nothing except the sun,the moon and all the stars. Scientists have always wanted to know more about the other worlds in the space.They have looked at them through telescopes and in this way they have found out a great deal.The moon is about 384 ,000 kilometers away from the earth.An airplane cann't fly to the moon but there is a thing that can fly even when there is no air. This is rocket.I am sure that you are asking,"How does a rocket fly?"If you want to know,get a balloon and then blow it up until it is quite big.Do not tie up the neck of the balloon.Let go!The balloon will fly off through the air very quickly.The air inside the balloon tries to get out.It rushes out through the neck of the balloon and this pushes the balloon through the air.It does not need wings like an airplane.This is how a rocket works.It is not made of rubber（橡胶）like a balloon,of course.It is made of metal. The metal must not be heavy but it must be very strong.There is gas inside the rocket which is made very hot. When it rushes out of the end of the rocket,the rocket is pushed up into the air.Rockets can fly far out into space.Rockets with men inside them have already reached the moon.Several rockets,without men inside them,have been sent to other worlds much farther away.One day rockets may be able to go anywhere in the space.A rocket can fly to the moon because______. A:it looks like a balloon B:it is much lighter than an airplaneC:it doesn't have wings D:it works like an untied balloon
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Weight on and off the Earth We are so used to.our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted.Because we can feel that things are heavy,we think of "weight"as being a fixed quality in an object,but it is not really fixed at all.If you could take a one-pound packet of butter 4,000 miles out from the earth,it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space?The reason is this:all objects have a natural attraction for all other objects;this is called gravitational attraction.But this power of attraction between two obects gets weaker as they get farther apart.When the butter was at the surface of the earth,it was 4,000 miles from the center.When we took the butter 4,000 miles out,it was 8,000 miles from the center,which is twice the distance.If you double the distance between two objects,their gravitational attraction decreases two times two.If you treble the distance, it gets nine times weaker(three times three)and so on. So this is one of the first things we need to remember that the weight of an object in space is not the same as its weight on the surface of the earth. What about the weight of our pound of butter on the surface of the moon?At the distance the puii of the earth is about 4,000 times smaller than it is here on the surface,so we can forget all about the earth-pull on our butter. On the other hand,on the moon there will be an attraction between the butter and the moon,but the butter will weigh only about one-sixth as much as it does on the earth.This is because the moon is so much smaller than the earth.The amount of gravitational pull that a body produces depends on the amount of material in it.A packet of butter has a gravitational pull of its own;but this is very small in relation to the pull of something as large as the moon,or the earth,or the sun.According to the passage,"weight"should be understood in the sense thatA:it is fixed if it is outside the earth's gravitational puliB:it decreases four times when it is 4,000 miles from the earth's centerC:it varies with the change of the gravitational attraction between two objectsD:things increase in amount as they are closer to the earth's surface
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Weight on and off the Earth We are so used to.our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted.Because we can feel that things are heavy,we think of "weight"as being a fixed quality in an object,but it is not really fixed at all.If you could take a one-pound packet of butter 4,000 miles out from the earth,it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space?The reason is this:all objects have a natural attraction for all other objects;this is called gravitational attraction.But this power of attraction between two obects gets weaker as they get farther apart.When the butter was at the surface of the earth,it was 4,000 miles from the center.When we took the butter 4,000 miles out,it was 8,000 miles from the center,which is twice the distance.If you double the distance between two objects,their gravitational attraction decreases two times two.If you treble the distance, it gets nine times weaker(three times three)and so on. So this is one of the first things we need to remember that the weight of an object in space is not the same as its weight on the surface of the earth. What about the weight of our pound of butter on the surface of the moon?At the distance the puii of the earth is about 4,000 times smaller than it is here on the surface,so we can forget all about the earth-pull on our butter. On the other hand,on the moon there will be an attraction between the butter and the moon,but the butter will weigh only about one-sixth as much as it does on the earth.This is because the moon is so much smaller than the earth.The amount of gravitational pull that a body produces depends on the amount of material in it.A packet of butter has a gravitational pull of its own;but this is very small in relation to the pull of something as large as the moon,or the earth,or the sun.How much would four pounds of tea weigh if it was taken 4,000 miles out from the surface of the earth?A:1 pound. B:2 pounds. C:3 pounds. D:4 pounds.
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Where Did the Earth's Water Come From?Earth is located within the"snow line"of the solar system,the region closest to the Sun where H2 0 is primarily in liquid or gaseous form,if at all.______(46)The snow line phenomena is reflected in the water content of planets like Mercury,Venus,and Mars. Water is absent on Mercury.On Venus,H2O only exists as a trace element in the atmosphere.Mars only has a thin veneer of ice in its polar regions.In general,water is rare within the snow line.Why does Earth have so much water relative to the other inner planets?71%of the surface is covered in the oceans,more than half of which is deeper than 3,000 meters,with an approximate total volume of 1.3 billion cu km.______(47)There are various theories as to where all the Earth's water came from,but several theories have fared better than the others.______(48)When the Earth was in the process of forming,with a radius just 40%smaller than at present,it would have had enough gravity to hold on to a tenuous atmosphere with water vapor. The first water vapor on the planet would have come from the planet's internals,where volatile(low weight)chemicals would have a tendency to float to the top,and heavy chemicals(iron and nickel)would sink.Though the first of Earth's water came about through volcanism,this alone probably didn't produce enough to form stable pools on the surface.______(49)Comparing the isotope ratios of water on Earth and water from comets and asteroids has revealed that the majority of the Earth's water comes from asteroids.Throughout its history,Earth's water has increased in volume due to biological processes. In the early seas of Earth,hydrogen sulfide would have been in great supply,which,when reacted with carbon dioxide from the atmosphere during photosynthesis in sulfide-reducing bacteria,would have produced hydrogen,sulfur,and water.______(50)________（49）A: More water was added to the planet during several hypothesized large impacts from asteroids from the outer asteroid belt.B:We know that the oceans existed as early as 100 million years after the formation of the Earth.C:Still,the oceans only make up 0.023%of the Earth's total mass.D:Astronomers say Earth s water may have come from space.E:The snow line is located in the outerasteroid belt,between the orbits of Mars and Jupiter. F: Many geologists believe that the majority of Earth's water generated through this process.
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Weight on and off the Earth We are so used to.our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted.Because we can feel that things are heavy,we think of "weight"as being a fixed quality in an object,but it is not really fixed at all.If you could take a one-pound packet of butter 4,000 miles out from the earth,it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space?The reason is this:all objects have a natural attraction for all other objects;this is called gravitational attraction.But this power of attraction between two obects gets weaker as they get farther apart.When the butter was at the surface of the earth,it was 4,000 miles from the center.When we took the butter 4,000 miles out,it was 8,000 miles from the center,which is twice the distance.If you double the distance between two objects,their gravitational attraction decreases two times two.If you treble the distance, it gets nine times weaker(three times three)and so on. So this is one of the first things we need to remember that the weight of an object in space is not the same as its weight on the surface of the earth. What about the weight of our pound of butter on the surface of the moon?At the distance the puii of the earth is about 4,000 times smaller than it is here on the surface,so we can forget all about the earth-pull on our butter. On the other hand,on the moon there will be an attraction between the butter and the moon,but the butter will weigh only about one-sixth as much as it does on the earth.This is because the moon is so much smaller than the earth.The amount of gravitational pull that a body produces depends on the amount of material in it.A packet of butter has a gravitational pull of its own;but this is very small in relation to the pull of something as large as the moon,or the earth,or the sun.We find it hard to break free from ideas connected with living on the earth because______.A:it demands too great an effort for us to do soB:we are too familiar with the way things are to question the ideasC:we have proved that those ideas are correctD:we are so sure of ourselves that we never doubt anything on the earth
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单选题According to the experts, the reversal of the Earth’s magnetic field would _____.A
destroy almost all the creatures on the EarthB
cause some species extinctions on the EarthC
not be as disastrous as the previous oneD
cause no big trouble for man and animals
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单选题While some military planners claimed that it would be possible to win a war fought with nuclear weapons, many scientists argued that such a war could not truly be won, because the fallout from nuclear warfare would create a nuclear winter and it also would be rendering the earth uninhabitable.A
it also would be rendering the earth uninhabitableB
rendering the earth uninhabitableC
might have uninhabitably rendered the earthD
render the earth uninhabitableE
would also have rendered the earth uninhabitable
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单选题If the earth suddenly_______ spinning，people would all fly off it.A
had stoppedB
stoppedC
has stoppedD
would stop
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单选题The author mentions that Marinnation would be all the following EXCEPT ______.A
a circular city attached to the seabedB
a home for international organizationsC
a monumental engineering taskD
a place where people would want to live
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单选题Many people_________ in the project at both research and editingstages and we would like to thank them all here.A
have involvedB
have been involvedC
having involvedD
having been involved
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