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   Up to 65% of children don't get as much sleep as they should do，and this can make them nervous and slower at school，scientists say.
   So how long should young people sleep each night？The answer is between eight and ten hours.If you don't get enough sleep at night，you'll have less energy the next day.
   But the scientists say many children have missed out on 4，500 hours of sleep by the time they are seven years old.They say that children miss sleep because they have TVs and computers in their rooms，and busy parents don't read to their younger children at night any more.The traditional "bedtime story" helps children to relax and fall asleep peacefully.Children with TVs and computers in their bedrooms are more likely to sleep badly，and to get less than eight hours' sleep.Even losing one hour's sleep a night can mean that children do less well at school.
   German scientists think that your brain keeps working while you are asleep.To show that they were right，they gave two groups of people a problem to work out.One group went to sleep，and the other group stayed awake.The result？The people who slept worked out the answer more quickly.This showed that their brains had been trying to find the answer while the people were asleep.So，make sure you get enough sleep tonight，and you'll be at your best tonight，and you'll be at your best tomorrow!
（1）What problem do more than a half of students have？
（2）What influences many children's sleep？
（3）What did the German scientists' experiment show？
（4）What is the purpose of the writer in writing the article？