Questions 16 to 20 are based on the following talk.
So, is everyone awake? I guess that's a good question at the start of an early morning lecture about sleep. Seriously, how many of you feel you didn't get enough sleep last night? Raise your hands! en… about a third of you. That's interesting, because it shows that you are not so different from the population in general. About 30% percent of adults say they frequently don't feel rested when they wake up in the morning. And why is that? Well, in most cases, it's because they stayed up too late partying or watching TV. But in a small percentage of cases, they could be suffering from a sleep disorder, a condition that interferes with a person's capability to sleep normally. There are many kinds of sleep disorders, but the three that I want to describe today are called sleep apnea, narcolepsy, and insomnia. Ok, the first sleep disorder that I listed is sleep apnea, that's a-p-n-e-a. People with sleep apnea stop breathing, sometimes for 10 seconds or longer, and not just once, it can happen several hundred times a night. Each time this happens, they wake up and go right back to sleep, so their sleep is constantly interrupted. But in the morning they don't remember waking up. They just feel tired and sleepy. Then how do you know if you have this problem? The usual symptoms are heavy breathing and snoring, combined with feeling tired all the time. The cause of this problem is that air can't go into and out of the nose or mouth, usually because the throat is too relaxed. Consequently, the treatment is very simple. The person wears a soft mask attached to a machine that helps to regulating his or her breathing throughout the night. In an extreme case of apnea, surgery may be necessary. The second sleep disorder that I want to describe today is called narcolepsy. That spells n-a-r-c-o-l-e-p-s-y. Perhaps you've seen a movie in which people are sitting at a table, eating and talking, and suddenly one person just falls over. Perhaps his face falls into his soup. It's funny in a movie, but in reality this could be a symptom of narcolepsy. Narcoleptic persons get sudden attacks of sleep, in the middle of the day, any time, any place. They can't control it. They simply fall asleep for brief periods of time. By the way, this disorder appears to be particularly frequent among students enrolled in 8 AM classes. But seriously, narcolepsy can be quite scary. The cause is high levels of certain chemicals in the part of brain that regulates sleep. Once narcolepsy is diagnosed, it's usually treated successfully with medication. Sleep apnea and narcolepsy are serious problems but they are real conditions. In contrast, the third sleep disorder I want to discus, insomnia, is quite common. Insomnia means difficulties either falling asleep or staying asleep. Almost everybody has insomnia once and a while. But I want to talk about chronic insomnia which when sleeping becomes difficult for weeks, months or years at a time. The cause could be either psychological or physical. Most often is psychological, that is, it is caused by stress, you know, worrying about problems at work or home and so on. Or the cause can be physical, such as too much caffeine or nicotine in the body. Both of these chemicals are stimulants that can keep you from sleeping. Stimulants are substances that make you feel awake and energetic. As I said, coffee and cigarettes are both stimulants. Now that brings us to treatments for insomnia. Obviously, if you have trouble sleeping, the first thing you should do is avoid coffee, tea and cigarettes in the evening. You should also avoid alcohol. Many people say that a glass of beer or wine helps them sleep. That may be true once in a while, but drinking alcohol every night is dangerous because after a while it stops working. And as everyone knows, alcohol is addictive. You should also avoiding sleeping pills for the same reason because they are addictive. These are the things you shouldn't do if you have insomnia. Now what should you do?

16. According to the lecturer, about what percentage of adults, say they often don't feel rested when they wake up in the morning?
17. The lecturer discus several types of sleep disorders, which of the following is not one of the disorders?
18．Which of the following is not a symptom of sleep apnea?
19．Which of the following is true with people who suffer from narcolepsy?
20．What can we learn from chronic insomnia?