第4部分：阅读理解（第31～45题，每题3分，共45分）
下面有3篇短文后有5道题。请根据短文内容，为每题定1个最佳选项。

Sleepwalking (梦游)

     Not all sleep is the same every night. We experience some deep, quiet sleep and some active sleep, which is when dreams happen. You might think sleepwalking would happen during active sleep, but a person isn't physically active during active sleep. Sleepwalking usually happens in the first few hours of sleep in the stage called slow-wave or deep sleep.
     Not all sleepwalkers actually walk. Some simply sit up or stand in bed or act like they're awake when in fact, they're asleep! Most, however, do get up and move around for a few seconds or for as long as half an hour.
     Sleepwalkers' eyes are open, but they don't see the same way they do when they're awake and often think they're in different rooms of the house or different places altogether'. Sleepwalkers tend to go back to bed on their own and they won't remember it in the morning.
     Researchers estimate that about 15% of kids sleepwalk regularly. Sleepwalking may run in families (在家族中世代相传) and sometimes occurs when a person is sick, has a fever, is not getting enough sleep, or is stressed (紧张).
     If sleepwalking occurs frequently, every night or so, it's a good idea for your mom or dad to take you to see your doctor. But occasional sleepwalking generally isn't something to worry about, although it may look funny or even scary (骇人的) for the people who see a sleepwalker in action.
     Although occasional sleepwalking isn't a big deal, it's important, of course, that the person is kept safe. Precautions (预防措施) should be taken so the person is less likely to fall down, run into something, or walk out the front door while sleepwalking.

31 When does sleepwalking usually occur?
     A　During active sleep,
     B　During deep sleep.
     C　In the daytime.
     D　In the early morning.

32 What most sleepwalkers do is
     A　simply sit up.
     B　simply stand in bed.
     C　get up and walk for some time
     D　get up and walk for hours

33 Sleepwalkers usually go back to bed
     A　after waking up.
     B　after being woken up.
     C　with the help of others.
     D　by themselves.

34 You'd better go and see a doctor if you
     A　see a sleepwalker in action.
     B　never sleepwalk,
     C　sleepwalk frequently.
     D　sleepwalk occasionally

35 Measures should be taken to
     A　keep sleepwalkers safe.
     B　prevent people from sleepwalking
     C　avoid running into sleepwalkers.
     D　help people sleep well.