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    Cloze 21
   
    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
   
    21. BCCBD  CADAB     CDABC  ADBCA