Sleep is divided into periods of so-called REM sleep, characterized by rapid eye movements and dreaming, and longer periods of non-REM sleep. 1 kind of sleep is at all well-understood, but REM sleep is 2 to serve some restorative function of the brain. The purpose of non-REM sleep is even more 3 . The new experiments, such as those 4 for the first time at a recent meeting of the Society for Sleep Research in Minneapolis, suggest fascinating explanations 5 non-REM sleep.

For example, it has long been known that total sleep 6 is 100 percent fatal to rats, yet, 7 examination of the dead bodies, the animals look completely normal. A researcher has now 8 the mystery of why the animals die. The rats 9 bacterial infections of the blood, 10 their immune systems – the self-protecting mechanism against diseases-had crashed.

Vitamins are organic compounds necessary in small amounts in the diet for the normal growth and maintenance of life of animals, including man. They do not provide energy, 11 do they construct or build any part of the body. They are needed for 12 foods into energy and body maintenance. There are thirteen or more of them, and if 13 is missing a deficiency disease becomes 14 . Vitamins are similar because they are made of the same elements – usually carbon, hydrogen, oxygen, and 15 nitrogen. They are different 16 their elements are arranged differently, and each vitamin 17 one or more specific functions in the body. 18 enough vitamins is essential to life, although the body has no nutritional use for 19 vitamins. Many people, 20 , believe in being on the “safe side” ad. thus take extra vitamins. However, a well-balanced diet will usually meet all the body’s vitamin needs.

1. A. Either B. Neither C. Each D. Any

2. A. intended B. required C. assumed D. inferred

3. A. subtle B. obvious C. mysterious D. doubtful

4.A. maintained B. described C. settled D. afforded

5. A. in the light of B. by virtue of C. with the exception of D. for the purpose of

6. A. reduction B. destruction C. deprivation D. restriction

7. A. upon B. by C. through D. with

8. A. paid attention to B. caught sight of

C. laid emphasis on D. cast light on

9. A. develop B. produce C. stimulate D. induce

10. A. if B. as if C. only if D. if only

11. A. either B. so C. nor D. never

12.A. shifting B. transferring C. altering D. transforming

13. A. any B. some C. anything D. something

14. A. serious B. apparent C. severe D. fatal

15. A. mostly B. partially C. sometimes D. rarely

16.A. in that B. so that C. such that D. except that

17. A. undertakes B. holds C. plays D. performs

18 A. Supplying B. Getting C. Providing D. Furnishing

19. A. exceptional B. exceeding C. excess D. external

20.A. nevertheless B. therefore C. moreover D. meanwhile

答案解析：BCCBD CADAB CDABC ADBCA

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