17．
Sleep is very important．A person who does not sleep dies faster than a person who does not eat．We spend about a third（1/3）of our lives in sleep．That's about 121 days a year!
How much sleep do we need？We are all different．A baby needs 16 hours of sleep every day．Children 6 to 12 years old need an average（平均） of 10 to 12 hours of sleep．Teenagers need 9 to 10 hours of sleep．An adult needs an average of 7 to 8hours a night．There are some people who need only 3 hours of sleep．Others need 10 hours of sleep．After the age of 50，the average sleep time goes down to 6.5 hours a night．We need less sleep as we get older．
About one in three Americans has a problem with sleep．Many of these people can not fall asleep．The name of this problem is insomnia．Some people say，"I didn't sleep all night．"But that's not really true．They may sleep lightly and wake up several times．In the morning，they only remember the times they were awake（醒着），so they think they were awake all night．
This is not a new problem．Many famous people in history had insomnia．Some of these people had special ideas to make them sleep．Benjamin Franklin had four beds．He moved from one to the other to fall asleep．Mark Twain had a different way．He lay on his side across the end of the bed!
77．If you are thirteen years old，you need at leastC hours of sleep．
A.16
B.12
C.9
D.7
78．What does"insomnia"mean in this passageA？
A．No sleep．
B．Bad sleep．
C．Slow sleep．
D．Sleep with many dreams．
79．Which of the following is true according to the passageB？
A．We will die soon if we don't sleep well．
B．The older we get，the less sleep we need．
C．We can tell a person's age from his sleep time．
D．Famous people move from one bed to the other to fall asleep．
80．Which would be the best title for this passageB？
A．Sleep More!
B．Go to Sleep!
C．Age and Sleep Time
D．Famous People and Sleep．
