All living creatures---people, animals, fish, even the tiniest insects---have a daily need for sleep or complete rest. Without a period of rest ___1___ periods of activity, the mind and body would become too fatigued to work properly. People who are deprived of (剥夺)sleep for a long time become irritable. They find it ___2___ to think clearly and concentrate on their work. Often they see or hear things that are not really there. The desire to sleep shows itself ___3___ drowsiness (困倦), heaviness and dryness of the eyelids, and difficulty in paying the attention fixeD. 来源：www.examda.com A sleeping person is unconscious --- unaware of what is going on ___4___ him. But unlike the unconsciousness that comes from fainting or injury, the unconsciousness of sleep can be quickly endeD. A strong shake or a loud noise, ___5___ as an alarm clock s ringing, will awaken most sleepers at once.
The vital organs cease to work during sleep, ___6___ body functions are slowed down. Breathing is slower and deeper. The heart beats ___7___ slowly, and blood pressure is lower. Arms and legs are soft and the muscles are at rest. Therefore it would be difficult for a person to achieve this ___8___ of relaxation during waking hours, and sleep offers better opportunity for recovery from fatigue than the most quiet rest.
The function of the body becomes lower during the hours ___9___ a person is usually asleep. A lowered body temperature makes a person feel chilly. This is why a person who is sleeping usually must be ___10___. People who are accustomed to waking up during the day and sleeping at night will have a 0drop in body temperature at night, even when they stay up all night.
1. A. involvingB. followingC. connectingD. preceding
2. A. convenientB. sensitiveC. easyD. difficult
3. A. over B. at C. by D. in
4. A. about B. aroundC. over D. through
5. A. so B. such C. as D. like 来源：www.examda.com 6. A. but B. so C. so thatD. and
7. A. much B. a little C. moreD. less
8. A. sense B. kindC. type D. degree
9. A. that B. which C. when D. in which
10. A. covered B. uncovered C. covering D. uncovering