问题
单项选择题
Questions 16 to 20 are based on the following talk.
A. Chronic insomnia is a rare condition compared with apnea or narcolepsy.
B. Almost everybody has chronic insomnia once in a while.
C. The cause for chronic insomnia is most often psychological.
D. There is no effective cure for this type of sleep disorder.
答案
参考答案：C
解析：
What can we learn about chronic insomnia