2011年六级完形填空分类练习（5）

会计考友

Sleep is divided into periods of so-called REM sleep, characterized by rapid eye movements and dreaming, and longer periods of non-REM sleep.    41    kind of sleep is at all well-understood, but REM sleep is   42   to serve some restorative function of the brain. The purpose of non-REM sleep is even more   43  . The new experiments, such as these   44   for the first time at a recent meeting of the Society for Sleep Research in Minneapolis, suggest fascinating explanations   45   of non-REM sleep.
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    For example, it has long been known that total sleep   46   is 100 percent fatal to rats, yet,   47   examination of the dead bodies, the animals look completely normal. A research has now   48   the mystery of why the animals die. The rats   49   bacterial infections of the blood,   50   their immune systems-the self-protecting mechanism against diseases-had crashed.
   
1 ~7 [! w) E9 K; c* f2 n) n    41. [A] Either [B] Neither [C] Each [D] Any
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$ }2 \' n+ s, H6 H7 J    42. [A] intended [B] required [C] assumed [D] inferred
   
    43. [A] subtle [B] obvious [C] mysterious [D] doubtful
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    44. [A] maintained [B] described [C] settled [D] afforded
   
    45. [A] in the light [B] by virtue [C] with the exception [D] for the purpose
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3 J  |4 l  Y& Z- m3 O    46. [A] reduction [B] destruction [C] deprivation [D] restriction
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    47. [A] upon [B] by [C] through [D] with
   
( ~: X! n8 Y2 }( S    48. [A] paid attention to [B] caught sight of [C] laid emphasis on [D] cast light on
   
. D+ Q2 S% d7 l8 [4 O- O6 C    49. [A] develop [B] produce [C] stimulate [D] induce
   
    50. [A] if [B] as if [C] only if [D] if only