2. 外语
  3. Small dogs generally live longer than big dogs so that small Yorkshire terrier(猎狐狗)next door could be around for a long time. Bu

Small dogs generally live longer than big dogs so that small Yorkshire terrier(猎狐狗)next door could be around for a long time. Bu

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问题     Small dogs generally live longer than big dogs so that small Yorkshire terrier(猎狐狗)next door could be around for a long time. But body size isn’t the only factor that【B1】______ how long dogs survive. Personality influences life span, too, according to a new study that might help explain how animal【B2】______ evolve.
    Study on animals from ants to apes has found that different【B3】______have different personalities. Some are timid, others【B4】______Biologists have proposed that temperaments(性情)evolved along with life history. Bold, violent animals use a lot of energy fast in【B5】______short lives, the thinking goes, whereas calmer animals last longer, saving themselves to【B6】______ later in life. But it’s hard to run evolutionary【B7】______on these personalities in anything longer lived than a fruit fly. So evolutionary biologist Vincent from Canada【B8】______an idea about dogs. "All these breed differences reflect an experiment on artificial selection," says Vincent. The huge diversity of dogs resulted not from natural selection, but from generations of humans selecting animals with traits—the ability to chase foxes into holes, or herd sheep, or sit【B9】______on a sofa.
    But evolutionary physiologist Joseph Williams of Ohio State University in Columbus isn’t convinced that what happened in dogs【B10】______evolution in nature. "For me, it still remains to be seen. Dogs are contrary to what you would expect in nature in terms of longevity," he says. Elephants can live for decades, whereas a mouse might make it through only for several seasons. On the other hand, a Chihuahua will generally outlast a Saint Bernard.
【B4】
选项
答案aggressive
解析 反义参照题。此空所填的词与timid词性相同，词义相对。既然有的“胆怯”，那么其他动物的性格应与“胆怯”正好相反。结合录音可知，答案为aggressive。
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