题目内容：

It is not unusual to see your desk-mate yawn (打呵欠) as he complains that he didn't have a good sleep the night before. Many teens don't get enough sleep because they have too much homework, which keeps them up at night. Some teens cannot sleep at night even when they want to.

Studies show that during your teenage years, the body's biological clock is reset, telling you to sleep later at night and wake up later in the morning.

But changes in the body clock aren't the only reason teens lose sleep. Lots of people have insomnia (失眠). The most common cause of insomnia is stress. But all sorts of things can lead to insomnia. These include physical discomfort, emotional troubles and even sleeping environment. It's common for everyone to have insomnia from time to time. But if it lasts for a month or more go and see a doctor.

Some people have a condition that causes stomach acid (酸) to move backward towards the chest. This produces the uncomfortable, burning feeling called heartburn. So even if the person doesn't notice the feelings of heartburn because he is sleeping, he may feel tired the next day.

Most teens have nightmares sometimes. But, if they are frequent, a person's sleep pattern can be seriously affected. The most common cause of nightmares is emotional problems, such as stress (压力) or anxiety. If you have them a lot, it's a good idea to talk to a doctor.

Doctors encourage teens to make lifestyle changes to develop good sleeping habits. You probably know that coffee can keep you awake, but did you know that playing video games or watching TV does the same?

1.The main idea of the first paragraph is ________.

A. There is a problem that teenagers can’t get enough sleep.

B. Sleeping problems have different causes.

C. Yawning is a good way to get rid of sleep.

D. Teenagers care too much for homework.

2.The Teenagers’ biological clock ________.

A. easily makes teenagers lead to insomnia

B. is the origin of their insomnia

C. provides them with plenty of time at night

D. is helpful to improve their concentration(注意力)

3.What does the writer say about “nightmares”?

A. It is nothing and shouldn’t be taken seriously.

B. It can release their stress or anxiety.

C. Emotional problems are the only way to form nightmares.

D. People will suffer from sleep if frequent.

4.Which way can help to get rid of insomnia?

A. Drinking some coffee before going to bed.

B. Playing video game or watching TV from time to time.

C. Turning to a doctor for help.

D. Eating much medicine for insomnia.