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单选题
Pistons of marine medium speed diesel engines may be made of （） in order to keep the weight down for balancing purpose at high speed.
A
lead
B
forged steel
C
alloy steel
D
aluminum alloy
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单选题（）diesel engines generally have two systems of lubrication:（）a total loss system feeding and a circulating system lubricating the running gear and cooling the pistons.A
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is usually cooled by sea waterB
can be replaced when worn outC
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单选题The majority of medium speed and high speed marine diesel engines for main or auxiliary drive operate on the （） cycle.A
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单选题In comparison to exhaust valves, intake valves of diesel engines may be fabricated from low alloy steels because （）.A
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单选题Pistons of marine medium speed diesel engines may be made of （） in order to keep the weight down for balancing purpose at high speed.A
leadB
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单选题The main bearing shells are made of steel with a lining of bearing metal which may be white metal, copper-lead or aluminum-tin alloy What is the meaning of “which” in the sentence above?（）A
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main bearingC
steelD
bearing metal
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单选题Typical marine propulsion plants include（） directly coupled to the vessel’s single large-diameter, fixed-pitch propeller.A
a single, long-stroke, slow-speed, turbocharged, two-stroke diesel engineB
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单选题An advantage of aluminum pistons, when compared to cast iron pistons is （）.A
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better heat conductivityC
greater weight per cubic inchD
increased resistance to wear
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