How much sleep is enough？
To stay in good health，some expert in the US say，adults should get seven to eight hours of sleep．Teenager need nine to ten hours．And pre﹣school children need more than 10 hours of sleep a night．
Experts say the quality（质量）of our sleep becomes poor as we grow older．This happens because the brain unit that controls sleep begins to weaken slowly as we age．
Experts say the change starts in our 30s．By the time we reach our 50s，a person may have lost 50 percent of their ability to have a restful sleep.
These people have trouble failing and staying asleep through the night．From middle age on，these problems only get worse，and they can have a bad effect on their health．
Signs that show you may not be getting enough sleep．
You're always hungry or you've got unwanted weight．If you are in short of sleep，certain chemicals in your body will not work well and tell your brain in time that you have eaten enough．
You have trouble making decisions．Not having enough sleep may make your brain work slower in problem solving．
You have trouble remembering things．Sleep helps prepare the brain for new memories．
Your feeling changes unreasonably．People who don't sleep well may feel unable to control their feelings．
You are having trouble seeing．If there is a shortage of sleep，you may not be able to see thing as clearly as usual．
How to improve your sleep？Here are a few things people can do to get better sleep．
Health experts say that exercise and avoiding work on computers make people go to sleep more easily．A cool room is also a good choice for sleeping well．
55．What can we learn from the passage？
| A． |
With the help of medicine，we can sleep better． |
| B． |
People begin to have sleep problems in their 40s． |
| C． |
Teenagers usually need more sleep than adults． |
| D． |
Few people have sleep problems in their late years． |
56．The underlined word"effect"in the passage is close in meaning to．
| A． |
Knowledge |
| B． |
influence |
| C． |
excuse |
| D． |
activity |
57．According to the passage，which of the following is NOT a sign that you are not sleeping well？
| A． |
You often get hungry． |
| B． |
Your eyesight is failing． |
| C． |
You have proper memory |
| D． |
You always feel tired． |
58．It is possible that the article is taken from．
| A． |
a middle﹣school textbook |
| B． |
a scientific report |
| C． |
A magazine on health |
| D． |
an ad in the newspaper． |
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