阅读理解。
Everyone must go to bed early and get up early, or we won't be healthy and clever.
Is this true? Perhaps it is. The body must have enough sleep. Children of your age need ten hours'
sleep every day. If you don't go to bed early, you won't have enough sleep. Then you can't think properly
and can't do your work properly. You'll not be clever.
Some people go to bed late and get up late. This is not good for them. We must sleep at night when it
is dark. The dark helps us to sleep soundly. When the daytime comes, we must get up. This is the time for
exercise. If you lack exercise, the body becomes weak.
Exercise keeps a strong body. Exercise helps the blood (血液) flow (流动) around inside the body. This
is very important. Blood takes food to all parts of our body. The brain also needs blood. We think with our
blood. If we keep our body healthy and take exercise, we can think better.
1. If we want to be healthy and clever, we must go to bed _____.
A. late and get up early
B. early and get up late
C. early and get up early
D. late and get up late
2. Children of your age need _____.
A. ten hours' sleep
B. nine hours' sleep
C. twelve hours' sleep
D. eleven hours' sleep
3. The best time to sleep is when _____.
A. daytime comes
B. it is dark
C. we are taking exercise
D. it is late afternoon
4. Exercise makes the body _____.
A. weak
B. clever
C. active
D. strong
5. Exercise _____.
A. makes more blood
B. helps the blood to flow
C. makes food for our blood
D. makes our brain tired
25受拉纵筋，则梁的抗弯承载力Mu=（）kN·m。