A、Because tryptophan can balance their diet. B、Because tryptophan is an amino acid found in certain foods. C、Because tryptophan

Recent studies of patients at sleep clinics have revealed significant facts about the causes of insomnia as well as ways to deal with it. It is no surprise that stress and depression are linked to insomnia.
    Also, insomnia may be caused by physical illness: itching, aches, asthma, arthritis, ulcer and heart problem that involve shortness of breath or difficulty in breathing.
    What can you do if you suffer from insomnia? Two things: you can eat certain foods that will help you fall sleep and stay asleep. And you can do certain things that are sleep-inducing. Here are some guidelines:
    A. If you had a bad night sleep, don’t stay in bed later than the next morning.
    B. Don’t go to bed earlier the next night, stick to your usual bedtime and rising pattern.
    C. Don’t nap during the day. Naps cut down on night sleep time.
    D. Never lie awake in bed for more than thirty minutes. By lying in bed sleepless, you can form an association between your bed and sleepless.
    E. Get as much exercise as possible, preferably in the morning.
    As for food intake to help you sleep, make sure that your diet is a balanced one and rich in tryptophan, an amino acid found in certain foods. The body can convert tryptophan to air tryptophan and then to serotonin, a body chemical crucial to the sleep process. If you include in your daily diet food high in tryptophan, such as apples, eggs, cheese, fish and meat and incorporate some of the sleep-inducing activities into your life, the chances are good that you will achieve a pattern of restful and suiting sleep.
16. What is the talk mainly about?
17. Which of the following is not mentioned as an illness inducing insomnia?
18. What is the speaker’s advice to insomniac who had a bad sleep?
19. Why are the insomniac advised to include food high in tryptophan in their daily diet?
20. What is the speaker’s attitude toward the future of the insomniac?