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  3. Mammals vary enormously in size, from weighing less than a penny to measuring more than three school buses in length. Some group

Mammals vary enormously in size, from weighing less than a penny to measuring more than three school buses in length. Some group

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问题     Mammals vary enormously in size, from weighing less than a penny to measuring more than three school buses in length. Some groups of mammals have become very large, such as elephants and whales,【C1】________others have always been small, like primates. A new theory developed by an international team, led by Jordan Okie,【C2】________an explanation for why and how【C3】________ groups of organisms are able to evolve【C4】________sizes, whereas others are not.
    The research team【C5】________information on how quickly an individual animal grows and used it to【C6】________how large it may get【C7】________evolutionary time. Their research was published recently.
    The new theory developed from the observation that some animals【C8】________fast and die young, while others take their time and mature much later. "Fast" animals-such as mice—breed very quickly, while humans mature slowly and are relatively older when they first have children. The theory【C9】________that those species that are relatively faster are more likely to evolve a large size quicker than slow species, and that their maximum size will be greater.
    The research team tested their theory using the【C10】________ records of mammals over the last 70 million years, examining the maximum size of each mammal group【C11】________ that time, including whales, elephants, seals and primates. They found that their theory was very well【C12】________.
    "Primates have evolved very slowly, and never got bigger than 1,000 pounds," said Okie, "The【C13】________was true of whales, which evolved their large size at the fastest【C14】________recorded."
    The theory also makes predictions about the relative risks of extinction for large animals【C15】________small. The maximum size of an animal is limited by the rate of mortality in the【C16】________. Because larger animals【C17】________ breed less frequently than smaller animals,【C18】________the mortality rate doubles, the maximum size is predicted to be 16 times smaller.
    "This is a really surprising【C19】________," said Okie. "It points to another reason why many of the large animals went【C20】________after the last Ice Age, and their high risk of extinction in modern environments."
【C7】
选项 A、for
B、before
C、over
D、by
答案C
解析 本空格需填入一个介词与evolutionary time“进化期”构成时间状语。C项over表示“在……期间”，符合语义。A项for后接“一段时间”，表示某事持续的时间。B项before和D项by代入后分别表示在进化期之前、到进化期为止能长成多大的体型，语义逻辑不对。
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