单选题According to the passage, the root cause for weather changes on the earth is ______.A the atmosphere surrounding the earthB water from oceans and lakesC energy from the sunD greenhouse gases in the sky

考题 According to the passage, which is true about the ocean?A. The waters of the ocean came from rain water.B. The ocean was formed from the, lighter rock materials.C. The vast single ocean formed about 200 million years ago.D. The ocean covered the whole surface of the earth at very beginning.

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考题 27． From the passage we know that fresh water doesn't come from________ ．A．riversB．lakesC．undergroundD．the sea

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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.

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考题 A greenhouse is a building made of glass which is used for keeping plants when the outside temperature is low. In a similar way there are several gases in the atmosphere which trap(捕捉)the heat produced by the sun and prevent it from escaping. These gases are known as"greenhouse gases"，and the way in which they trap heat in the atmosphere is called the "greenhouse effect". This is not simply air pollution. Most of the main greenhouse gases exist naturally in small amounts in our atmosphere, and without them earth would be 30 degrees colder and human life would not exist. In other words, the greenhouse effect is a natural course which is to some degree helpful to us.The problem is that in the last century and a half, we have been putting too many of these gases into the earth's atmosphere by burning large quantities of coal and oil and by cutting down forests. The rapid increase in greenhouse gases is making the world warmer. The world's temperature has already gone up by half a degree this century, and the sea level has risen by 10 centimetres. If the amount of carbon dioxide(二氧化碳)in the atmosphere doubles, there will probably be a rise in the earth's temperature of between 1 and 4 degrees. This may seem a small increase, but it would be enough to cause major changes in geography and agriculture. Large areas of the world would be flooded, and some areas would become dry and unable to produce crops. It is important, too, to consider that there may be a delay of about 30 years in the greenhouse effect. This means that we are probably experiencing only now the effect of the gases put into the atmosphere before the 1960s. Since then, our use of these gases has greatly increased.1. The"greenhouse effect"means _____.A. the way in which gases are used for keeping plants warmB. a natural course which is some degree helpful to usC. the way"greenhouse gases"trap heat on the earthD. the whole course in which greenhouse gases prevent heat2. If there were no greenhouse effect, _____.A. no plants would grow on our planetB. earth would be thirty degrees colderC. man could not live on the earthD. All of the above answers are correct3. Which of the following is NOT true? _____A. Burning too much coal and oil produces lots of greenhouse gases.B. It has become warmer on the earth now than in the past.C. Gases put into the atmosphere now will affect the earth years later.D. The temperature in a greenhouse is as high as that in the atmosphere.4. Suppose the earth's temperature rose by 3 degrees, _____.A. great harm would be done to mankindB. the sea level would go by 10 centimetresC. all the land in the world would be floodedD. crops would be unable to grow on the earth5. This passage mainly deals with _____.A. the concept(概念)and harm of greenhouse effectB. the relation between greenhouse gases and manC. the concept and change of greenhouse effectD. the effect of the rise of the earth's temperature

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考题 In a()boiler the hot gases from the furnace pass gases from the furnace pass water is on the outside. A.water-tubeB.fire-tubeC.exhaust gasD.composite

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考题共用题干第三篇Preserve the EnvironmentThroughout history man has changed his physical environment in order to improve his way of life.With the tools of technology he has altered many physical features of the earth.He has transformed woodlands into farmland,and made lakes and reservoirs out of rivers for irrigation purposes or hydroelectric power. Man has also modified the face of the earth by draining marshes and cutting through mountains tobuild roads and railways.However,man's changes to the physical environment have not always had beneficial results.Today, pollution of the air and water is an increasing danger to the health of the planet.Each day thousands of tons of gases come out of the exhausts of motor vehicles;smoke from factories pollutes the air of industrialized areas and the surrounding areas of countryside.The air in cities is becoming increasingly unhealthy.The pollution of water is equally harmful.In the sea,pollution from oil is increasing and is killing enor- mous numbers of algae（水藻）,fish and birds.The whole ecological balance of the sea is being changed. The same problem exists in rivers.Industrial wastes have already made many rivers lifeless.Conservationists believe that it is now necessary for man to limit the growth of technology in order to sur-vive on earth.According to the passage,pollution of the air and water is caused by__________.A:thousands of tons of gases coming out of the exhausts of motor vehiclesB:the changes of the environment that technology has brought to manC:the increasing amount of oil that has been producedD:industrial wastes discharged into rivers

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考题共用题干第二篇Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO2).Car emissions are a major problem, but the truth is that more CO2 comes from the energy used at home.The average household creates aroundfive and a half tonnes of CO2 a year,and it is the same CO2 that is changing the climate and damaging the environment.CO2 and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO2 and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.In 2008,the total UK CO2 emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO2 emissions.These figures show that a significant amount of CO2 results from ordinary citizens carbon footprint in their daily activities and lifestyle.The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．CO2 emissions from vehicles_______.A:are a more serious problem than energy shortageB:do not cause any problemsC:are high because the average household owns a carD:contribute considerably to greenhouse gases

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考题共用题干第二篇Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO2).Car emissions are a major problem, but the truth is that more CO2 comes from the energy used at home.The average household creates aroundfive and a half tonnes of CO2 a year,and it is the same CO2 that is changing the climate and damaging the environment.CO2 and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO2 and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.In 2008,the total UK CO2 emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO2 emissions.These figures show that a significant amount of CO2 results from ordinary citizens carbon footprint in their daily activities and lifestyle.The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．What is the author's opinion about the level of CO2 emissions in the UK?A:The majority of CO2 emissions come from motorized transport.B:CO2 emissions may cause climate change in the future.C:More CO2 emissions come from homes than from cars.D:The average citizen does not create much CO2.

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考题共用题干第二篇Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO2).Car emissions are a major problem, but the truth is that more CO2 comes from the energy used at home.The average household creates aroundfive and a half tonnes of CO2 a year,and it is the same CO2 that is changing the climate and damaging the environment.CO2 and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO2 and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.In 2008,the total UK CO2 emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO2 emissions.These figures show that a significant amount of CO2 results from ordinary citizens carbon footprint in their daily activities and lifestyle.The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．Which of the following is the best title for the passage?A:Ways of reducing the UK's CO2 emissions.B:UK citizen's carbon footprint.C:The effect of industry on climate change in the UK.D:Changes in weather patterns in the UK.

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考题共用题干第二篇Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO2).Car emissions are a major problem, but the truth is that more CO2 comes from the energy used at home.The average household creates aroundfive and a half tonnes of CO2 a year,and it is the same CO2 that is changing the climate and damaging the environment.CO2 and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO2 and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.In 2008,the total UK CO2 emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO2 emissions.These figures show that a significant amount of CO2 results from ordinary citizens carbon footprint in their daily activities and lifestyle.The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．The results of climate change in the UK can be seen in______.A:cooler summersB:water supplyC:warmer wintersD:stronger winds

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考题共用题干第二篇Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO2).Car emissions are a major problem, but the truth is that more CO2 comes from the energy used at home.The average household creates aroundfive and a half tonnes of CO2 a year,and it is the same CO2 that is changing the climate and damaging the environment.CO2 and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO2 and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.In 2008,the total UK CO2 emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO2 emissions.These figures show that a significant amount of CO2 results from ordinary citizens carbon footprint in their daily activities and lifestyle.The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．What is the author's main aim?A:To explain the greenhouse effect.B:To describe the effects of climate change in the UK.C:To show how much CO2 is produced by ordinary people's activities.D:To illustrate how industrial activity creates the greenhouse effect.

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考题共用题干第一篇The Northern LightsThe sun is stormy and has its own kind of weather.It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour.These particles are called plasma （等离子体）,and the stream of plasma coming from the Sun is called the solar wind.The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth.When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into tile Earth's atmosphere at the poles.As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky.Each atmospheric gas glows a different color.Oxygen and nitrogen glows red and green arid nitrogen glows violet purple.As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras（北极光）is fun and exciting, but normally you can only see them in places far north like Alaska and Canada.The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate（跳动）,flicker（闪烁）,or even move like waves.During solar maximum,5 auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly.A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime.We know you will never forget it!The solar wind comes into being as a result of_______.A:disappearance of the Sun's gravityB:unpredictable weather of the SunC:fast flow of energy away from the SunD:a stream of particles being blown away

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考题共用题干第一篇Water Resources on the EarthThe second most important constituent（构成成分）of the biosphere（生物圈）is liquid water. This can only exist in a very narrow range of temperatures,since water freezes at 0℃and boils a 100℃．Life as we know it would only be possible on the surface of a planet which had temperature: somewhere within this narrow range.The earth's supply of water probably remains fairly constant in quantity.The total quantity of water is not known very accurately,but it is about enough to cover the surface of the globe to a depth of about two and three-quarter kilometers.Most of it is in the form of the salt water of the oceans一about 97 percent. The rest is fresh.But three-quarters of this is in the form of ice at the poles and or mountains and cannot be used by living systems until melted.Of the remaining fraction,which h somewhat less than one percent of the whole.There is 10—20 times as much stored underground water as there is actually on the surface.There is also a tiny,but extremely important fraction of the water supply which is present as water vapour in the atmosphere.Water vapour in the atmosphere is the channel through which the whole water circulation（循环） of the biosphere has to pass.Water evaporated（蒸发）from the surface of the oceans,from lakes and rivers and from moist（潮湿的）earth is added to it. From it the water comes out again as rain or snow,falling on either the sea or the land. There is,as might be expected, a more intensive evaporation per unit area over the sea and oceans than over the land,but there is more rainfall over the land than over the oceans and the balance is restored by the run off from the land in the form of rivers.The word"fraction"in the second paragraph means________.A:a large areaB:a very small amountC:an important systemD:a major source of information

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考题共用题干第一篇Water Resources on the EarthThe second most important constituent（构成成分）of the biosphere（生物圈）is liquid water. This can only exist in a very narrow range of temperatures,since water freezes at 0℃and boils a 100℃．Life as we know it would only be possible on the surface of a planet which had temperature: somewhere within this narrow range.The earth's supply of water probably remains fairly constant in quantity.The total quantity of water is not known very accurately,but it is about enough to cover the surface of the globe to a depth of about two and three-quarter kilometers.Most of it is in the form of the salt water of the oceans一about 97 percent. The rest is fresh.But three-quarters of this is in the form of ice at the poles and or mountains and cannot be used by living systems until melted.Of the remaining fraction,which h somewhat less than one percent of the whole.There is 10—20 times as much stored underground water as there is actually on the surface.There is also a tiny,but extremely important fraction of the water supply which is present as water vapour in the atmosphere.Water vapour in the atmosphere is the channel through which the whole water circulation（循环） of the biosphere has to pass.Water evaporated（蒸发）from the surface of the oceans,from lakes and rivers and from moist（潮湿的）earth is added to it. From it the water comes out again as rain or snow,falling on either the sea or the land. There is,as might be expected, a more intensive evaporation per unit area over the sea and oceans than over the land,but there is more rainfall over the land than over the oceans and the balance is restored by the run off from the land in the form of rivers.Most of the fresh water on Earth________.A:is in the form of ice at the poles and on mountainsB:is stored undergroundC:is found in rivers and lakesD:comes from the rain

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考题共用题干第一篇Water Resources on the EarthThe second most important constituent（构成成分）of the biosphere（生物圈）is liquid water. This can only exist in a very narrow range of temperatures,since water freezes at 0℃and boils a 100℃．Life as we know it would only be possible on the surface of a planet which had temperature: somewhere within this narrow range.The earth's supply of water probably remains fairly constant in quantity.The total quantity of water is not known very accurately,but it is about enough to cover the surface of the globe to a depth of about two and three-quarter kilometers.Most of it is in the form of the salt water of the oceans一about 97 percent. The rest is fresh.But three-quarters of this is in the form of ice at the poles and or mountains and cannot be used by living systems until melted.Of the remaining fraction,which h somewhat less than one percent of the whole.There is 10—20 times as much stored underground water as there is actually on the surface.There is also a tiny,but extremely important fraction of the water supply which is present as water vapour in the atmosphere.Water vapour in the atmosphere is the channel through which the whole water circulation（循环） of the biosphere has to pass.Water evaporated（蒸发）from the surface of the oceans,from lakes and rivers and from moist（潮湿的）earth is added to it. From it the water comes out again as rain or snow,falling on either the sea or the land. There is,as might be expected, a more intensive evaporation per unit area over the sea and oceans than over the land,but there is more rainfall over the land than over the oceans and the balance is restored by the run off from the land in the form of rivers.Liquid water only exists________.A: in the center of the earthB:on the surface of our planetC:in the coastal areas of the earthD:in a very narrow range of temperatures

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考题共用题干第一篇Water Resources on the EarthThe second most important constituent（构成成分）of the biosphere（生物圈）is liquid water. This can only exist in a very narrow range of temperatures,since water freezes at 0℃and boils a 100℃．Life as we know it would only be possible on the surface of a planet which had temperature: somewhere within this narrow range.The earth's supply of water probably remains fairly constant in quantity.The total quantity of water is not known very accurately,but it is about enough to cover the surface of the globe to a depth of about two and three-quarter kilometers.Most of it is in the form of the salt water of the oceans一about 97 percent. The rest is fresh.But three-quarters of this is in the form of ice at the poles and or mountains and cannot be used by living systems until melted.Of the remaining fraction,which h somewhat less than one percent of the whole.There is 10—20 times as much stored underground water as there is actually on the surface.There is also a tiny,but extremely important fraction of the water supply which is present as water vapour in the atmosphere.Water vapour in the atmosphere is the channel through which the whole water circulation（循环） of the biosphere has to pass.Water evaporated（蒸发）from the surface of the oceans,from lakes and rivers and from moist（潮湿的）earth is added to it. From it the water comes out again as rain or snow,falling on either the sea or the land. There is,as might be expected, a more intensive evaporation per unit area over the sea and oceans than over the land,but there is more rainfall over the land than over the oceans and the balance is restored by the run off from the land in the form of rivers.There is more of rainfall________.A:over the mountains than over the riversB:over the rivers than over the mountainsC:over the land than over the oceansD:over the oceans than over the land

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考题共用题干第一篇Water Resources on the EarthThe second most important constituent（构成成分）of the biosphere（生物圈）is liquid water. This can only exist in a very narrow range of temperatures,since water freezes at 0℃and boils a 100℃．Life as we know it would only be possible on the surface of a planet which had temperature: somewhere within this narrow range.The earth's supply of water probably remains fairly constant in quantity.The total quantity of water is not known very accurately,but it is about enough to cover the surface of the globe to a depth of about two and three-quarter kilometers.Most of it is in the form of the salt water of the oceans一about 97 percent. The rest is fresh.But three-quarters of this is in the form of ice at the poles and or mountains and cannot be used by living systems until melted.Of the remaining fraction,which h somewhat less than one percent of the whole.There is 10—20 times as much stored underground water as there is actually on the surface.There is also a tiny,but extremely important fraction of the water supply which is present as water vapour in the atmosphere.Water vapour in the atmosphere is the channel through which the whole water circulation（循环） of the biosphere has to pass.Water evaporated（蒸发）from the surface of the oceans,from lakes and rivers and from moist（潮湿的）earth is added to it. From it the water comes out again as rain or snow,falling on either the sea or the land. There is,as might be expected, a more intensive evaporation per unit area over the sea and oceans than over the land,but there is more rainfall over the land than over the oceans and the balance is restored by the run off from the land in the form of rivers.The total quantity of water on Earth________.A:has greatly increased in recent yearsB:remains almost unchangedC:is decreasing constantlyD:is affected by global warming

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考题共用题干 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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考题 Water transport occurs on inland waterways，such as（），and oceans.A、riversB、lakesC、canalsD、land

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考题单选题_____ to flow spontaneously from a block of ice to a surrounding volume of water, this could occur in complete accord with energy conservation.A There were energyB There was energyC Were energyD If energy is

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考题单选题A definite advantage of using water as a fire extiguishing agent is its characteristic of（）.A alternate expansion and contraction as water in a liquid state becomes a vaporB absorption of smoke and gases as water is converted from a liquid to a vaporC rapid contraction as water is converted from a liquid to a vaporD rapid expansion as water absorbs heat and changes to steam

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考题填空题By increasing the levels of greenhouse gases in the atmosphere, human activities are strengthening Earth’s natural greenhouse effect.____

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考题单选题According to the passage, the greatest part of the solar energy that reaches the Earth is _____.A reflected back to space by snow and iceB concentrated at visible wavelengthsC absorbed by carbon dioxide moleculesD absorbed by atmospheric water vapor

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考题单选题______ to flow spontaneously from a block of ice to a surrounding volume of water, this could occur in complete accord with energy conservation.A There were energy B There was energyC Were energyD If energy is

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考题单选题Only a small part of the sun’s energy reaches the earth’ s surface because most of it is ______.A absorbed by the clouds in the lower atmosphereB reflected by the gases in the upper atmosphereC lost in the upper and lower atmosphereD used to evaporate water from the oceans and lakes

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考题单选题We learn from the passage that ______.A all living things on the earth depend on the sun for their foodB a forest looks dark in winter because it absorbs solar energyC only 0.023 of the energy from the sun is made use of on the earthD greenhouse gases allow heat energy to escape from the earth’ s surface

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考题单选题We can infer from the passage that quakes ______.A may happen anywhere at any timeB mostly strike in oceans and mountainsC are unobservable in masses of landD are hardly the direct cause of fatalities

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