Fire, scientists agree, helped give rise to a successful, thriving human population by providing heat for cooking and protection

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问题     Fire, scientists agree, helped give rise to a successful, thriving human population by providing heat for cooking and protection from the cold.
    But they don’t agree【C1】______when humans began using fire. Some researchers argue that it【C2】______more than a million years ago when early humans【C3】______their way to Europe from Africa, and【C4】______say it happened much later. Now, a new study reveals that humans did not【C5】______fire until about 400 000 years ago.
    Two archaeologists(考古学家)in the US report their【C6】______in the current issue of the Proceedings of the National Academy of Sciences. They looked at excavation(发掘)reports and studies from 141 sites in Europe that were【C7】______1.2 million and 35 000 years old. They think there is no clear evidence of【C8】______fire use until about 400 000 years ago. In Africa,【C9】______there are several sites where there was evidence of fire, those may have been【C10】______fires that occurred in the African grassland.【C11】______, there are also sites older than 400 000 years in Europe that indicate the【C12】______of humans, with the oldest, in Spain, more than a million years old. This means that【C13】______Europe’s extreme winter climates, early humans found a way to【C14】______without the warmth of a fire.【C15】______the researchers mention, early humans are【C16】______and persistent(坚持的). But some researchers【C17】______that it is still a puzzling explanation and it still【C18】______some serious thinking about how【C19】______the human being could have survived on a seasonally【C20】______food supply despite having small teeth and small guts. Up to now, no one has solved this problem yet.
【C9】

选项 A、while
B、when
C、since
D、provided

答案A

解析 上一句指出没有发现用火的证据,本句又提到在非洲发观几处火的痕迹,很显然这是一种转折关系,所以选while引导让步状语从句,意为“虽然,尽管”when引导时间状语从句;since“由于;自……以后”,引导原因或者时间状语从句;provided“假如,倘若”,引导条件状语从句。
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