Question

Most of us spend a third of our lives sleeping. Scientists have been studying the brain to learn what happens while we sleep. Scientists tell us that there are four stages(阶段)of sleep. During each stage our brain behaves differently, and so does our body. Each stage is marked by changes in the pattern of brain waves, which can be recorded by machines.

In the first stage, we drift off to sleep. Our muscles(肌肉)begin to relax. Our heartbeat and breathing slow down. Body temperature and blood pressure(压力)begin to drop. Stage—two sleep is a time of small, fast brain waves. Our eyes move quickly from side to side as if watching a movie. This is known as rapid eye movement, or REM sleep. During REM sleep, dreaming takes place. In stage three the brain wave becomes slower again.

Within about 45 minutes after falling sleep, we progress into the fourth stage – deep sleep. As this happens, our brain sends out slower but larger brain waves. This is the most restful kind of sleep, but it is also the time when sleepers are most likely to change positions or sleepwalk. After deep sleep we return to stage two. As the hours pass, we repeat the sleep cycle four or five times. Then we wake up.

1.How many stages of sleep do we repeat several times during a night?

A.Two. B.Three. C.Four. D.Five.

2.When does a person most likely change his positions?

A.When first falling asleep. B.During stage three.

C.During REM sleep. D.During deep sleep.

3.Which of the following statements is TRUE?

A.We can dream in all the stages of sleep, especially during REM sleep.

B.It is impossible to record the pattern of our brain waves with machines.

C.Our body, like our brain, behaves differently during each stage of sleep.

D.It takes about 45 minutes to complete the sleep cycle after we fall asleep.

Answer 1