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根据下列材料，请回答题

Sleep

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 down a bit t00，with the alpha rhythm of rather fast waves predominating for the first few minutes_____ （47）For the next half hour or so，as you relax more and more，you will drift down 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．Your 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．but instead about 80 minutes after you fall into slumber，your brain activity level will increase again slightly．_____ （49）Your eyes will begin to dart around under your closed eyelids as if you were l00-king at something occurring in front of you _____ （50）It is during 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 l to stage 4 sleep—only to rise once again to the surface of near consciousness some 80 minutes later．

回答（46）题 查看材料

A.The delta rhythm will disappear，to be replaced by the activity pattern of brain waves．

B.If you are an average sleeper，your sleep cycle is as follows．

C.In stage 4 sleep people tend to dream．

D.The lower your stage of sleep，the slower your brain waves will be．

E.This period of rapid eye movement lasts for some 8 to 1 5 minutes and is called REM sleep．

F.This is called stage l sleep．

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