阅读理解
   There is an old English saying.It tells us that we must go to bed early and get up early in the morning.Then we shall be healthy.We shall also be rich and clever.This is true.The body must have enough sleep to be healthy.Children of young age should have ten hours' sleep every night.Children who do not have enough sleep cannot do their work well and they may not be healthy.The body also needs exercise.Walking, running, jumping and playing games are all exercise.Exercise keeps the body strong.Exercise also helps the blood to move around inside the body.It is very important.Our blood moves to all parts of our body.The head also needs blood.Exercise helps us to think better.

如图是人体的关节模式图，请据图回答下列问题：