请根据以下内容回答下列各题 After a day' s hard work, we needsome sleep. During the sleep,

the fatigue (疲劳)of the body disappears and recuperation (恢复)begins. The tired mind gathers new energy, and the memory improves. Some adults require little sleep;others need eight to ten hours in every twenty-four hours. Infants (婴儿) sleep sixteen toeighteen hours daily, the amount gradually diminishing as they grow older.Young students may need twelve hours; university students may need ten. Aworker with a physically demanding job may also need ten, whereas an executiveworking under great pressure may manage on six to eight. Many famous people have little sleep. Napoleon Bonaparte, Thomas Edison and Charles Darwinapparently averaged only four to six hours a night. Whatever your individual need,you can be sure that by the age of thirty you will have slept for a total ofmore than twelve years. By that age you will also have developed a sleeproutine: a favorite hour, a favorite~ bed, a favorite position, and a rule youneed to follow in order to rest comfortably. Investigators have tried to findout how long a person can go without sleep. Several people have reached morethan 115 hours--nearly five days. Whatever the limit, it is absolute. Animalsthat kept awake for from five to eight days have died of exhaustion. The limitfor human beings is probably about a week. Bywriting this passage, the writer intends to tell us that __________

A. sleep is important for good mental andphysical health

B. a light sleep is as restful as a deepsleep

C. memory is improved during sleep

D. sleep is relatively unimportant for humanbeings