The Earth’ s daily clock, measured in a single revolution, is twenty-four hours. The human clock,【C1】______, is actually about t

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问题     The Earth’ s daily clock, measured in a single revolution, is twenty-four hours. The human clock,【C1】______, is actually about twenty-five hours. That’ s 【C2】______ scientists who study sleep have determined from human subjects who live for several weeks in observation chambers with no【C3】______of day or night. Sleep researchers have 【C4】______ other surprising discoveries as well.
    We spend about one-third of our lives asleep, a fact that suggests sleeping, 【C5】______ eating and breathing, is a fundamental life process. Yet some people almost never sleep, getting by on as 【C6】______ as fifteen minutes a day. And more than seventy years of【C7】______into sleep deprivation, in which people have been kept【C8】______for three to ten days, has 【C9】______ only one certain finding: Sleep loss makes a person sleepy and that’ s about all; it causes no lasting ill【C10】______. Too much sleep, however, may be【C11】______for you.
    These findings【C12】______some long-held views of sleep, and they【C13】______questions about its fundamental purpose in our lives. In【C14】______, scientists don’t know just why sleep is necessary..
    Some scientists think sleep is more the result of evolutionary habit than【C15】______actual need, Animals sleep for some parts of the day perhaps because it is the 【C16】______ thing for them to do: it keeps them【C17】______and hidden from predators; it’s a survival tactic. Before the advent of electricity, humans had to spend at least some of each day in【C18】______and had little reason to question the reason or need for【C19】______. But the development of the electroencephalograph and the resulting discovery in 1937 of dramatic【C20】______in brain activity between sleep and wakefulness opened the way for scientific inquiry in the subject.
【C16】

选项 A、worst
B、best
C、only
D、natural

答案B

解析 考查形容词辨析。此处句意为“动物在一天中的某些时候睡觉,可能是因为睡觉对于它们来说是一的事”。根据下文的hidden from predators(躲开食肉动物),it’s a survival tactic(这是一条生存策略)可知B.best符合题意,为正确答案。
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