Fallingasleepisaroutineprocess.However,thoughmostofusfa...

问题详情：

Falling asleep is a routine process. However, though most of us fall asleep every night, we can’t say exactly how we do it. Like trying to see the 3-D image in a Magic Eye poster, the more you focus on it, the less likely it is to happen.

According to recent work by neuroscientists at Washington University, during the pre-sleep stage of the process , you're in bed with the lights off and your eyes closed, slowly "letting go" of the trials of the trials of the day. In this period the brain progressively disengages(脱离) from the outside world.

Then, at some crucial moment, you enter the transitional sleep stage, known as stage 1. Brain waves slow down, but you can occasionally sense that you’re still awake. Investigators asked subjects awoken from various stages of sleep whether they considered themselves asleep. Only about 10 percent of those aroused from stage 1 said that they had been asleep."

Next, your brain moves on to stage 2, the start of "true" non-REM (rapid eye movement) sleep—REM sleep is the stage when most dreams occur. All neuroscientists agree that this stage is sleep, though you still might not know it. In that same study of sleep arousal, about 60 percent believed that they had been asleep when awoken from stage 2. The other 40 percent would tell you they hadn't fallen asleep yet.

Next, we enter slow-wave sleep (also known as deep sleep, or stages 3 and 4), and finally, experience the REM sleep period. While stages 1 and 2 are difficult to notice, 90 percent of people recognize themselves as having definitely fallen asleep when awoken after entering stages 3 or 4. That means we've completed the transition. From then on, we spend the rest of the night circling between non-REM stages 2, 3 and 4, and REM sleep.

32. What does the author use 3-D image to show?

A. It is hard to fall asleep. B. Falling asleep is a routine thing.

C We cannot focus on falling asleep. D. Falling asleep is a puzzling process.

33. Why are subjects woken up during the process of falling asleep?

A. To instruct them to sleep well. B. To check if they thought they were asleep.

C. To prevent them from deep sleep. D. To remind them they were doing experiments.

34. At which stage do we have dreams?

A. REM sleep. B. Stage 1. C. Slow-wave sleep D. Stage 2.

35. What happens after we complete the process of falling asleep?

A. We have deep sleep all night. B. We wake up and feel energetic.

C. We repeat from stage 2 to REM sleep. D. We return to the transitional sleep stage.

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