题目内容：

    A new study says the habit of sleeping in（睡懒觉）on weekends may not be such a good idea for your health.

36 healthy young men and women took part in the study. They were divided into three groups and were followed over 30 days.

The first group could sleep for nine hours each night for the 30 days. The second group had other only five hours of sleep every night. The third group had five hours on weekdays but was allowed to sleep as long as they wanted on the weekend. But on Monday, the third group was put back to the sleep schedule（周期）of only five hours a night.

The study showed that the first and the third groups ate more snacks after dinner and put on weight during the study, men much more than women.

What was surprising the scientists was the third group who slept in on weekends. "Even though people slept as much as they could, it was not enough," Dr. Wright said. "As soon as they went back to the short sleep schedules on Monday, the ability of their body to control blood sugar was badly affected." "Not only that, the result showed increased sensitivity to insulin（胰岛素）in both their muscles（肌肉）and their livers（肝脏）, the result wasn't found in other groups. The reason may be that their body clock had been changed.

1.How many groups were the people divided into in the study?

A.3 B.4 C.5 D.6

2.How long did the third group sleep everyday？

A.5 hours everyday.

B.9 hours everyday.

C.9 hours on weekdays and 5 hours on weekends.

D.5 hours on weekdays and sleep as long as they wanted on weekends.

3.From the study we know that __________.

A.women put on more weight than men

B.the sleep-deprived（睡眠不足的）people were more healthy

C.the second group didn't put on weight

D.women ate more snacks after dinner

4.What happened to the members in the third group?

A.Their blood sugar was badly affected.

B.They had enough sleep.

C.They didn't change their body clock.

D.They had increased sensitivity to insulin in hand.

5.What does the passage mainly tell us?

A.Sleeping is not important.

B.Sleeping too much on weekends may not be good for our health.

C.We can change our body clock as often as we can.

D.Adults don't need too much sleep.