2. 外语
  3. Sleep is part of a person’s daily activity cycle. There are several different stages of sleep, and they too occur in cycles.(46)

Sleep is part of a person’s daily activity cycle. There are several different stages of sleep, and they too occur in cycles.(46)

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问题 Sleep is part of a person’s daily activity cycle. There are several different stages of sleep, and they too occur in cycles.(46). When you first drift off into slumber, your eyes will roll about a bit, your temperature will drop slightly, your muscles will relax, and your breathing will slow and become quite regular. Your brain waves slow a bit too, with the alpha rhythm of rather fast waves predominating for the first few minutes.(47). For the nest half hour or so, as you relax more and more, you will drift clown through stage 2 and stage 3 sleep.(48). Then, about 40 to 60 minutes after you lose consciousness, you will have reached the deepest sleep of all. You brain waves will show the large slow waves that are known as the delta rhythm. This is stage 4 sleep.
You do not remain at this deep fourth stage all night long.(49). The delta rhythm will disappear, to be replaced by the activity pattern of brain waves. Your eyes will begin to dart around under your closed eyelids as if you were looking at something occurring in front of you.(50). It is during REM sleep that most dreams seem to occur. Provided that you do not wake up during the first REM sleep period, your body will soon relax again, your breathing will grow slow and regular once more, and you will slip gently back from stage 1 to stage 4 sleep—only to rise once again to the surface of near consciousness some 80 minutes later.

A.This is called stage Ⅰ sleep.
B.If you are an average sleeper, your sleep cycle is as follows.
C.But instead about 80 minutes after you fall into slumber, your brain activity level will increase again slightly.
D.Sleep is very useful for a person’s health.
E.This period of rapid eye movement lasts for some 8 to 15 minutes and is called REM sleep.
F.The lower your stage of sleep, the slower your brain waves will be.
选项
答案B
解析 下文开始介绍当人入睡后的情况，这里需要一个过渡，而B中的as follows表明该句放入这里最合适。
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