听力原文： So, is everyone awake? I guess that's a good question at the start of an early-morning lecture about sleep. About 30% of adults say they frequently don't feel rested when they wake up in the morning. And why is that? Why, in most cases it is 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, er— a condition that interferes with a person's ability to sleep normally. There are many different kinds of sleep disorders but the three I want to describe today are called sleep apnea, narcolepsy and insomnia. OK, the first disorder I list 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. The usual symptoms are heavy breathing and snoring, combined with feeling tired all the time. The second sleep disorder I want to describe today is called narcolepsy. That's spelled 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 a.m. classes. But seriously, narcolepsy can be quite scary. Sleep apnea and narcolepsy are serious problems, hut they are rare conditions. In contrast, the third disorder I want to discuss, insomnia, is quite common. Insomnia means difficulty either falling asleep or staying asleep. Almost everybody has insomnia once in a while. But I want to talk about chronic insomnia, which is when sleeping becomes difficult for weeks, months, or years at a time. The cause could be either psychological or physical. Most often, it's psychological that is, it's caused by stress—you know, worrying about problems at work or at home and so on. Or the cause could be physical such as too much caffeine or nicotine in the body. Both of these chemicals are stimulants that can keep you from sleeping. So, in summary, the thing I want you to remember is that everyone suffers from occasional sleeping problems, but a large number of people suffer from serious sleep disorders such as insomnia, apnea, and narcolepsy. As you've heard, these disorders have distinct symptoms, causes and treatment. Thanks to a lot of research in this area in the last few decades, doctors are now about to send patients to special sleep disorder clinics for specialized treatment. Since human beings spend one third of our lives sleeping, we should all be glad that medical science is now able to help people with sleeping problems. Questions： 16. What is the talk mainly about? 17.Which of the following statements is TRUE about apnea? 18.What is the symptom of narcolepsy? 19.What is the definition of insomnia? 20.Which of the following statements is TRUE about sleep disorders? (36)