英语六级考试完形填空分类练习5

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.

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.

41. ［A］ Either ［B］ Neither ［C］ Each ［D］ Any

42. ［A］ intended ［B］ required ［C］ assumed ［D］ inferred

43. ［A］ subtle ［B］ obvious ［C］ mysterious ［D］ doubtful

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

46. ［A］ reduction ［B］ destruction ［C］ deprivation ［D］ restriction

47. ［A］ upon ［B］ by ［C］ through ［D］ with

48. ［A］ paid attention to ［B］ caught sight of ［C］ laid emphasis on ［D］ cast light on

49. ［A］ develop ［B］ produce ［C］ stimulate ［D］ induce

50. ［A］ if ［B］ as if ［C］ only if ［D］ if only