What was the origin of the oil which now drives our motorcars and aircraft? Scientists are【C1】______about the【C2】______of coal,

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问题     What was the origin of the oil which now drives our motorcars and aircraft? Scientists are【C1】______about the【C2】______of coal, but they do not seem so【C3】______when asked about oil. They think that the oil【C4】______the surface of the earth originated in the【C5】______past, and was formed【C6】______living things in the sea. Countless billions of【C7】______sea creatures and plants lived and【C8】______to the sea bed. They were covered with huge【C9】______of mud; and by【C10】______of chemistry, pressure and temperature were changed through long【C11】______into what we know as oil. For these creatures to become oil, it was necessary that they should be【C12】______between layers of rock for an enormous【C13】______of time. The【C14】______that oil originated in the sea is【C15】______by a glance at a map【C16】______the chief oil fields of the world; very【C17】______of them are far distant from the oceans of today. In some places gas and oil【C18】______to the surface of the sea from its bed. The rocks in which oil is found are【C19】______marine origin too. They are sedimentary rocks, rocks which were【C20】______by the action of water on the ocean.
【C13】

选项 A、period
B、length
C、extension
D、exhibition

答案B

解析
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