单选题：Sleep　　Sleep is part of a person’s daily activity cycle．Ther

　　Sleep
　　Sleep is part of a person’s daily activity cycle．There are several different stages of sleep，and they too Occur in cycles．If you are an average sleeper，your sleep cycle is as(______1)．When you first drift out into slumber(睡眠)，your eyes will roll about a bit，your temperature will(______2)slightly，your muscles will relax，and your breathing will slow and become quite(______3)．Your brain waves slow down a bit t00，with the alpha rhythm of rather fast waves predominating for the first few minutes．This is called Stage l sleep．For the next half hour(______4)，as you relax more and more，you will drift down through Stage 2 and Stage 3 sleep．The lower your stage of sleep，the(______5)．your brain waves will be． Then，about 40 t0 60 minutes after you lost (______6)，you will have reached the deepest sleep of all．Your brain waves will show the large slow waves that are known(______7)the delta rhythm．This is Stage 4 sleep．
　　You do not remain at this deep fourth stage all night lon9，but instead，about 80 minutes after you fall into slumber，your brain activity level will(______8)again slightly．This delta rhythm will(______9)，to be replaced by the activity(______10)of brain waves．Your eyes will begin to turn around under your closed eyelids as if you were looking at something occurring in front of you．This period of rapid eye movement lasts for (______11)8 to 1 5 minutes and is called REM sleep．It is during REM sleep (______12)most dreams seem to occur． (______13)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(______14)gently back from Stage l to 4 sleep only to(______15)once again to the surface of near consciousness 80 minutes later．请选择（1）处的最佳答案． A．followed
B．so
C．follows
D．mentioned