The Earth’s daily clock, measured in a single revolution, is twenty-four hours. The human clock, 【B1】______ , is actually about

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问题     The Earth’s daily clock, measured in a single revolution, is twenty-four hours. The human clock, 【B1】______ , is actually about twenty-five hours. That’s 【B2】______ scientists who study sleep have determined from human subjects who live for several weeks in observation chambers with no 【B3】______ of day or night. Sleep researchers have 【B4】______ other surprising discoveries as well.
    We spend about one-third of our lives asleep, a fact that suggests sleeping, 【B5】______ eating and breathing, is fundamental life process. Yet some people almost never sleep, getting by on as 【B6】______ as fifteen minutes a day. And more than seventy years of 【B7】______ into sleep deprivation, in which people have been kept 【B8】______ for three to ten days, has yielded only one certain findings: Sleep loss makes a person sleepy and that’s about all; it causes no lasting ill 【B9】______ . Too much sleep, however, may be 【B10】______ for you.
    These findings 【B11】______ some long-held views of sleep, and they raise questions about its fundamental purpose in our lives. In 【B12】______ , scientists don’t know just why sleep is necessary.
    "We get sleepy, and when we sleep, that sleepiness is reversed," Dr. Howard Roffwarg of the University of Texas in Dallas explains. "We know sleep has a function, 【B13】______ we feel it has a function. We can’t put our finger on it, but it must, 【B14】______ in some way, direct or indirect, have to do with rest and restitution."
    Other scientists think sleep is more the result of evolutionary habit than 【B15】______ actual need. Animals sleep for some parts of the day perhaps because it is the 【B16】______ thing for them to do: it keeps them 【B17】______ 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 【B18】______ and had little reason to question the reason or need for 【B19】______ But the development of the electroencephalograph and the resulting discovery in 1937 of dramatic 【B20】______ in brain activity between sleep and wakefulness opened the way for scientific inquiry in the subject.
【B16】

选项 A、worst
B、best
C、only
D、natural

答案B

解析 本题考查上下文推理。根据下文“睡觉使它们______,躲开食肉动物”,我们可选出正确答案B。相关部分的意思是:“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最好的事,……”
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