英語填空答案
as,as,closed,cyclical,Instead,rapidly,sound,then,though,waking During a night's sleep we do not merely fall into progressively deeper sleep and then gradually wake up.[11] ,our brain waves show a [12] pattern that repeats about every 90 minutes.First we fall into deeper and deeper sleep,but [13] we gradually return to a " [14] " pattern.At this point,[15] ,we do not wake up,[16] might be expected.Instead,we remain [17] asleep and our eyes move [18] back and forth under our [19] eyelids.This stage is known [20] REM sleep.The average person has about four or five episodes of REM sleep each night,totaling about 25 percent of sleep time,or from one and a half to two hours.