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."
单选题
【C1】
【正确答案】
B
【答案解析】解析：文章开头提到不同哺乳动物的体型差别极大(vary enormously in size)。上一句提到“有些种类的哺乳动物变得非常大”，接着在空格后表明“有些一直都很小”。因此空格处应是表对比关系的逻辑词，答案只能选B项while“然而”。
【答案解析】解析：空格后的词组groups of organisms表示“生物群体”，与上文提到的Some groups of mammals“有些种类的哺乳动物”语义对应。A项certain与some一样，可以用作泛指形容词．与名词连用表示未加具体说明的人、地、物，可翻译作“某些”。
单选题
【C4】
【正确答案】
A
【答案解析】解析：本空格需填入一个形容词修饰sizes，与上文提到的不同哺乳动物体型有大有小相对应，所以只能选择表示大小的形容词，分别对应上文的large和small。另外谓语部分是are able to evolve“能够进化”，根据常识可知，动物进化的过程是由小型进化成大型的，所以A项gigantic“巨大的”符合语义逻辑。
单选题
【C5】
【正确答案】
D
【答案解析】解析：本句所填入的谓语应能作用于其宾语“关于单个个体的成长时间的信息(information on how．．．grows)”，体现主语the research team与宾语的关系。D项examined“仔细观察，研究”代入后表示该小组仔细研究了单个个体的成长时间的信息。
单选题
【C6】
【正确答案】
B
【答案解析】解析：根据后面句子里的情态动词may可知，后面的内容谈论的是可能性。也就是说，单个个体能长得多大(how large it may get)是根据其成长时间的信息进行预测的，而不是研究得出的结论，故用B项predict“预测”。