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No one knows why we sleep, but it’s certain that we need to. People who are prevented from sleeping begin to suffer obvious effects after a few days—they think less clearly, and they fall asleep during the working hours. There are no rules about sleep. Generally speaking, grown-ups sleep about 7 and a half hours each night and probably more than 60 percent get between seven and eight hours. But perhaps eight percent are quite happy with 5 hours or less, and four percent or so find that they want ten hours or more. If you feel all right, you’re probably getting enough sleep. The important thing is not to worry how much other people get—their needs may be different. Exercise doesn’t seem to increase the need for sleep—office workers, for example, sleep for about as long as people doing physically active work. Children sleep more than grown-ups—perhaps 14 to 18 hours soon after birth, going down to grown-up levels by early teenage (青少年). Sleep patterns also tend (倾向) to be different in the old people, who may sleep less at night than they did when younger, find sleep getting more broken, and often make it a rule to sleep during the daytime. 1. Some people can’t think clearly because _______. A. they have bad memory B. they feel sleepy during the working hours C. they don’t have enough sleep D. they are certain to be kept from going to bed 2. Whether you have got enough sleep is judged (判断) by _______. A. how many hours you have slept B. how many hours you need to sleep C. if you do exercise and physical work D. if you feel fresh energetic 3. According to the passage, a boy of 14 years old sleeps _____. A.as long hours as a grown-up B. much longer hours than a grown-up C. for 14 hours each night D. for less than 8 hours each night 4. Which of the following is True? A. All grown-ups much have at least eight-hour sleep. B. Most of grown-ups sleep for seven or eight hours. C. Quite a few people need only 5 hours or less for them to sleep. D. No grown-ups sleep more than ten hours.
【答案与解析】睡觉要占去人一生三分之一左右的时间。人为什么要睡觉？这个问题一直使人们，包括科学家在内，都困惑不解。本文向读者介绍了不同年龄层次的人们，睡眠的需求也不尽相同。 1.C.A、B两个答案是睡眠的结果而不是导致人们思维不清的主要原因，故不能选，D也不能说明原因。由第二段我们知道，睡眠不足是引起人们思维混乱的根本原因。 2. B.短文的第二段有交待：60%以上的成年人大约睡7-8小时。 3. D.判断人们是否得到足够的睡眠不是根据睡眠时间的长短而是人们是否精神焕发地去从事一天的工作与学习。 4. A. 14岁的孩子属于early teenage. 他们的睡眠时间与成年人相同。故答案为A。
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