9．Do you get enough sleep？With so much homework，it's often difficult to get the rest you need．But you need to try，because sleep keeps you healthy and it stops you from getting fat．Recently，a group of US scientists did a study of kids aged between 8and 13．The study found that if kids sleep for just one extra hour each day，the chance of their getting fat is cut by about 30percent．
Why？When people don't get enoughsleep，they become tired．When they are tired，they don't exercise enough．Also，kids ike snacks．If they are awake（醒） one more hour or two each day，they have more time to eat snacks or other unhealthy foods．
So，how much sleep should you get？Scientists suggest（建；議） 10to 11hours a night for kids aged 5to 12．For older kids，eight to nine hours will do．
39．How many reasons are given why people might get fat without enough sleep？B
A.3．
B.2．
C.1．
D．None．
40．What does"eight to nine hours will do"mean？A
A．Eight to nine hours'sleep will be good and enough．
B．Eight to nine hours'sleep will be too long．
C．Eight to nine hours'sleep will help get fat．
D．Eight to nine hours'sleep will help eat snacks and unhealthy foods．：
41．What does the passage talk about？C
A．How to get long sleep．
B．How to keep fat．
C．Enough sleep makes people healthy and slim．
D．Long sleep make people healthy and slim．
