In the past few decades, remarkable findings have been made in ethology, the study of animal social behavior. Earlier scientists had【C1】______ that nonhuman social life was almost totally instinctive or fixed by genetics. Much more careful observation has shown that【C2】______ variation occurs among the social ties of most species, showing that learning is a part of social life. That is, the statuses are not solely fixed by the genes.【C3】______ , the learning that occurs is often at an early age in a process that is called imprinting. Imprinting is clearly not instinctive, but it is not quite like the learning of humans; it is something in between the two. An illustration best【C4】______ the nature of imprinting. Once, biologists thought that ducklings followed the mother duck because of instincts. Now we know that, shortly after they hatch, ducklings fix【C5】______ any object about the size of a duck and will henceforth follow it. So ducklings may follow a basketball or a briefcase if these are【C6】______ for the mother duck at the time when imprinting occurs. Thus, social ties can be considerably【C7】______ , even ones that have a considerable base【C8】______ by genetics. Even among the social insects something like imprinting must influence social behavior. For example, biologists once thought bees communicated with others purely【C9】______ instinct. But, in examining a "dance" that bees do to indicate the distance and direction of a pollen source, observers found that bees raised in isolation could not communicate effectively. At a higher level, the genetic base seems to be much more for an all-purpose learning rather than the more specific responses of imprinting. Chimpanzees, for instance, generally【C10】______ very good mother but Jane Goodall reports that some chimps carry the infant upside down or otherwise fail to nurture the young.

【正确答案】 A

【答案解析】解析：assume意为“假定，设想”，多用于未证实的假定，根据题意，“早期的科学家，假定非人类动物的社会生活几乎完全是天生的，或是由遗传决定的”，所以A项为正确答案。B项adopt意为“采用，接受”；C项believe意为“相信”；D项surmise意为“猜测，推测”，相当于“guess”。如：She surmised as such．(她如此猜测。)

【正确答案】 D

【答案解析】解析：A项What’s more可表示递进；B项Hence意为“因此，所以”，表示因果关系。文中上一段提到“学习是动物的社会生活的一部分”，第二段接着讲“学习发生在动物小时候的印象中期”，两段间不存在递进或因果关系。But在表转折时一般不与句子分开，所以D项However为正确答案。

【正确答案】 A

【答案解析】解析：A项clarifies意为“使清楚，阐明”，如：The government has time and again clarified its position on equal pay for women．(政府已经反复阐明政府对男女同工同酬的立场。)B项classifies意为“分类，使……成为机密”。C项defines意为“下定义，界定”。D项outlines意为“画轮廓，拟大纲”。根据原文的意思：“一个例证很好地阐明了‘印象’的本质”。所以A项clarifies为最佳答案。

【正确答案】 B

【答案解析】解析：此处可翻译为：“如果在‘印象’发生时，用篮球或公文包代替母鸭，小鸭子也许会跟随它们。”B项substituted意为“替代；调换(常与for连用)”，如：substituted A for B，意为“用A代替B”。appropriated是“拨作(款项等)供专用”，如：The government appropriated a large sum of money for building schools．(政府拨出一大笔钱修建学校。)assigned意为“指派”；distributed意为“分发，分配”。只有B选项符合题意，所以B为正确答案。

【正确答案】 D

【答案解析】解析：D项altered意为“改变，更改”，相当于change，符合题意。A项varied意为“变化，使不同(强调范围变化)”，vary from…to…“从……到……不等；在……到……之间”，如：The temperature varies from time to time．(温度常常变化。)B项deviated意为“越出正轨，违反"。C项differed意为“使相异”。