Do you know the reason why we feel tired in the middle of a class？Maybe you would say it is because the teacher's class is boring（1）

D

D

Perhaps this is something you have not paid enough attention to or not yet noticed.
   Purpose of sleep
   （2）

B

B

Sleep helps our body heal （修復(fù)），grow；and stay healthy.It also gives us energy，so we can be active all day.Doctors and health scientists say：When you close your eyes and need to rest，sleep is just the very best!This is more than advice.
   Sleep time
   Enough sleep is important to us.How much sleep do we need？New-born babies seep most of the time.They can sleep 20～22 hours a day.Children need 10 -12 hours of sleep a day.Teenagers need 8～10 hours of sleep a day because they need lots of energy to grow into their adult（成人的） bodies.Grown-ups usually need 6- 8 hours of sleep to keep active. （3）

E

E

That is why old people sleep less than young people.
   Interesting facts
   Almost everyone has their dreams while they sleep，but not all of them can tell their dreams clearly when they wake up. （4）

C

C

.More surprisingly，some may even get up in their dreams and walk around.This is called "sleepwalking".Are you a sleepwalker？Or，is there a sleepwalker around you？
   （5）

A

A

   It's not just people that love to snooze （打盹） .In fact，many animals have unusual or surprising sleeping habits.Some animals，such as bears and hedgehogs，sleep all through winter.The swift is a very fast bird that can sleep while it flies!Cute koalas sleep around 18 hours a day.Giraffes don't need much sleep at all.They usually sleep standing up.

A.Sleepy animals. B.Why do we need sleep？ C.Some people talk in their dreams. D.However，the real reason is probably that we don't have enough sleep. E.The older you get the less sleep you will need. F.Some people never dream while they sleep.