（1）If students can't get enough sleep，they will feel

in class.
A.tired
B.excited
C.active
（2）Children need at least

of sleep every night.
A.10 hours
B.9 hours
C.6.5 hours
（3）After age fifty，the sleep time

.
A.has no difference
B.goes up
 C.goes down
（4）Mark Twain，the famous American writer，

.
A.moved from one bed to another to fall asleep
B.had 413 beds and hoped to fall asleep in one of them
C.never slept on his bed