题目内容：

    It's no surprise that a night without enough sleep can lead to a bad morning.Does it also do harm to our bodies?

According to US sleep researcher David Dinges, not getting enough sleep can have serious side effects on our minds and bodies.

For the study, Dinges divided some people into three groups.The first group was allowed eight hours of sleep for two weeks;the second group was given six hours;the third group got four hours of sleep.

Dinges found that the people in the first group stayed normal while the people in the last two groups showed tiredness and negative feelings.

"When people don't have enough sleep,it’s hard to sense their happiness,"Dinges said."Also,they are less able to sense others' good feelings."

But if not having enough sleep can harm our health,can we get better later on?

“People think that sleep is like the bank that you can pay off your debt (债务)*at a later point in time,Us Sleep Scientist Matthew Walker told popular Science."But we now know that sleep is not like that.

According to Live Science,humans are the only animal species that don't have sleep storage (储存)systems,our brains（大脑）*cannot get back what we have lost.

So Scientists suggest that no matter how busy people are,they should always try to get enough sleep.

Here's the recommended*(建设)hours of sleep by age.Preschoolers(3 to 5 years):10 to 13 hours.School—age children(6 to 13 years):9 to 11 hours .Teenagers(14 to 17 years):8 to 10 hours.Adults(18 to 64 years):7 to 9 hours.Older adults(over 65 years):7 to 8 hours.

1.To get enough sleep,a five—year—old boy should go to bed before _______and get up at seven in the morning.

A.9:00 p.m. B.9:30 p.m. C.10:00 p.m. D.10:30 p.m.

2.According to the passage,if someone doesn't get enough sleep,he _______

A.can feel better after a good sleep later B.cannot return to a good condition

C.will need much time to get well again D.can still stay active for several days

3.A person with negative feelings always _______ .

A.shows interest in many things B.wants to share funny things

C.sees the dark side of something D.pays attention to others' good feelings

4.Which can be the best title of the passage?

A.The Importance of Sleep B.When to Get a Sleep

C.The Right Ways to Sleep D.A Research on Sleep Problems