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

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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.
【B1】

选项 A、however
B、furthermore
C、likewise
D、therefore

答案A

解析 本题考查逻辑关系。根据上下文的意思以及提示词actually,可以判断出本句与上句是转折关系。所以,正确答案是A。
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