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.

【正确答案】 B

【答案解析】解析：本题考查逻辑关系。句子的谓语是is，空格处缺的必然是一个连词或关系词。what是关系代词，在从句中作宾语；because是连词，表示原因。根据前后句的逻辑关系，正确选项是B。在本句中，what引导的这个表语从句比较复杂。who study sleep是定语从句，修饰主语scientists；定语从句who live for several weeks…day or night修饰先行词human subjects。

【正确答案】 C

【答案解析】解析：本题考查近义词辨析。四个选项都可以和into搭配，都含“调查，研究，探索”的意思。probe是新闻用语，指广泛而彻底的调查；investigation指详尽的调查，以弄清事实真相；research指科学家为了发现新的事实从原始资料开始进行的调查或研究；examination强调详细观察或检验某事以求了解其真实情况。据此C符合句意。

【正确答案】 A

【答案解析】解析：本题考查上下文推理。at least意为“至少”；at most意为“最多”；at best意为“充其量，至多”；at worst意为“在最坏／最不利的情况下”。根据常识和上下文，我们知道睡眠和休息复原是有关系的。所以，首先排除B和C。这里讨论的是睡日民与休息复原的关系，不存在什么最坏最好情况的假设，所以D也排除。正确答案是A。句意是：“虽然我们不能准确地指出睡眠的功用，但它肯定至少在某些方面，与休息和复原有着直接或间接的关系。”