Insomnia is the inability to fall asleep or sleep restfully. It is a problem to nearly everyone at some time. A person may be awake for an hour in the middle of the night and then, next morning, feel that he hardly slept all night. Normally, worrying about not getting enough sleep is the worst aspect of most insomnia. If insomnia is recurrent, however, it is important to find its possible causes and try to correct them, with the help of a doctor if necessary.
A large number of factors may make it difficult for someone to fall asleep or remain asleep. His mattress may be too soft or too hard. The bedroom itself may be overheated or too cold. If it is not dark enough, or too noisy, this may cause difficulty in sleeping. Eating shortly before going to bed may also be responsible for insomnia. Stimulating drinks, such as tea or coffee, can also keep people awake.
Inability to fall asleep is sometimes a symptom of emotional or mental disorders. Insomnia may also be caused by pain and, very rarely, it can be a symptom of a physical disease.
The cause of insomnia may be easy to correct. The sufferer should check the mattress, bedroom temperature, and make any necessary changes, He should relax for an hour or two before bedtime, perhaps by reading a book, watching television or taking a warm bath. If he wakes during the night, he should try turning on the light and reading for a while. Above all, he should try not to worry about sleeplessness.
If necessary, a doctor may prescribe tranquillizers (镇静剂) or sleeping pills. Take only the dosage he prescribes; any more is erous.From the text, we can infer that if one can't fall asleep, it might be because of（）

A．the quality of his bedroom
B．eating before going to bed in two hours
C．overhappiness or sorrow
D．he didn't take a warm bath before going to bed

Insomnia is the inability to fall asleep or sleep restfully. It is a problem to nearly everyone at some time. A person may be awake for an hour in the middle of the night and then, next morning, feel that he hardly slept all night. Normally, worrying about not getting enough sleep is the worst aspect of most insomnia. If insomnia is recurrent, however, it is important to find its possible causes and try to correct them, with the help of a doctor if necessary.

B.
A large number of factors may make it difficult for someone to fall asleep or remain asleep. His mattress may be too soft or too hard. The bedroom itself may be overheated or too cold. If it is not dark enough, or too noisy, this may cause difficulty in sleeping. Eating shortly before going to bed may also be responsible for insomnia. Stimulating drinks, such as tea or coffee, can also keep people awake.

C.
Inability to fall asleep is sometimes a symptom of emotional or mental disorders. Insomnia may also be caused by pain and, very rarely, it can be a symptom of a physical disease.

D.
The cause of insomnia may be easy to correct. The sufferer should check the mattress, bedroom temperature, and make any necessary changes, He should relax for an hour or two before bedtime, perhaps by reading a book, watching television or taking a warm bath. If he wakes during the night, he should try turning on the light and reading for a while. Above all, he should try not to worry about sleeplessness.