13．
March 21is World Sleep Day．How's your sleep recently？
The Chinese Medical Doctor Association asked 8，200people in China about their sleep．More than 36.3percent of them said they often sleep badly．The study also finds that many students have only 5hours of sleep a day．According to the US National Sleep Foundation，teenagers need 8.5to 9hours of sleep every night．
What cuts into their sleeping time？Homework．Also，school starts early in the morning．But bad sleeping habits also play a role．
Do you like to have a look at your mobile phone before going to bed？The survey finds that 60percent of people check their phones before they sleep．They read news，check their WeChat （微信） and micro blog（博客） messages，or chat with QQ friends．
It's important for us to get enough sleep．If we can't get enough sleep，we'll feel sleepy and think slowly．And sleepy kids are often unhappy，says a study by the US National Sleep Foundation．
We can't change our school time．But there are still ways to get better sleep．Stay away from soda，coffee and tea at night．They make it hard to sleep well．Leave your mobile phone and computer on your desk．Watch less TV．
Look at these numbers in the box．They are glycemic indexes （血糖生成指数）．The bigger the number is，the better that food can help you to get better sleep．
44．How many hours of sleep do teenagers need every night according to the passage？B
A．About 12hours B．About 9hours C．About 4hours D．About 5hours
45．Many students can't get enough sleep becauseD．
A．they play sports too much and feel tired
B．they use mobile phones during the day time
C．they drink too much soda，coffee and tea at night
D．they have too much homework and bad sleeping habits
46．When people can't get enough sleep，they mayA．
A．feel sleepy and unhappy B．go to bed earlier next day
C．change their school time D．go to work late next day
47．In the passage if you want to get better sleep，you shouldB．
A．chat with your friends B．eat the right food
C．put your phone beside you D．be away from food like dates．
