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  3. No one knows exactly why we sleep. But scientists have learned a lot about how we sleep. When you first fall asleep, your hea

No one knows exactly why we sleep. But scientists have learned a lot about how we sleep. When you first fall asleep, your hea

admin2012-05-08  33
问题    No one knows exactly why we sleep. But scientists have learned a lot about how we sleep.
   When you first fall asleep, your heart starts to beat more slowly and your breathing slows down. If something wakes you, you might not think that you had been asleep. Some people call it dozing (打盹). Next, you enter into a deeper sleep. Your pulse (脉搏) and breathing become even slower. But you can still be awakened quite easily. If you take a catnap, you probably will not get any further than this stage (阶段) of sleep. If you sleep longer than about twenty minutes, you get into the third one. Your body is very relaxed. It would take a loud noise to wake you up. You may have heard of people who walk in their sleep. No one knows what makes people sleepwalk. But a person can sleepwalk only during stage four. This is the last and deepest kind of sleep. If someone wakes you up, you might feel very uncomfortable and you need a few minutes to get used to being awake. After about ten minutes of this stage sleep, you go back to stage three and then to stage two. Then something quite different begins to happen. Your heartbeat becomes rapid. Your eyelids flutter (颤动), and your eyes move. This stage of sleep is called REM (rapid eye movement) sleep.
   Most dreams happen during REM sleep. Scientists who study dreams often make noises or talk to sleeping people in the REM stage. They are trying to find out what effects noises can have on dreams, what causes dreams and how dreams might be helpful to people.
The following phenomena might happen when one sleeps. Which happens last during his non-REM sleep?
选项 A、Sleepwalking.
B、Nap.
C、Doze.
D、Dream.
答案A
解析 根据第二段的描述，一个人的睡眠经过第一、二、三个阶段到第四阶段，第四阶段是睡眠最沉的一个阶段，并且会发生梦游的现象。第四阶段后，睡眠又进入到第三和第二阶段，这一阶段被称为REM，也就是说第一到第四阶段是non-REM。由以上分析可以看出，non-REM阶段中最后可能发生的现象是“梦游”，故A是正确答案。
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