It is not unusual to see your deskmate 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.Lost 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．teenager can’t get enough sleep at all
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
3．Which way can help to get rid of insomnia?
A．Drinking some coffee before going to bed.
B．Playing video games or watching TV often.
C．Turning to a doctor for help.
D．Eating much medicine for insomnia.
1．A [段落大意题。根据第一段“It is not unusual to see your deskmate yawn...Some teens cannot sleep at night even when they want to.”可知，青少年们无法获得足够的睡眠。]
2．A [细节理解题。根据第二段的“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.”可知，青少年们的生物钟容易导致他们失眠。]
3．C [细节理解题。根据倒数第二段的“If you have them a lot，it’s a good idea to talk to a doctor.”和最后一段的信息可知选C。]