Sleep is divided into periods of so-called REM sleep， characterized by rapid eye movements and dreaming， and longer periods of non-REM sleep. kind of sleep is at all well-understood， but REM sleep is to serve some restorative function of the brain. The purpose of non-REM sleep is even more . The new experiments， such as these for the first time at a recent meeting of the Society for Sleep Research in Minneapolis， suggest fascinating explanations of non-REM sleep.
For example， it has long been known that total sleep is 100 percent fatal to rats， yet， examination of the dead bodies， the animals look completely normal. A research has now the mystery of why the animals die. The rats bacterial infections of the blood， their immune systems-the self-protecting mechanism against diseases-had crashed.
41. [A] Either Neither [C] Each [D] Any
42. [A] intended [B] required assumed [D] inferred
43. [A] subtle [B] obviousmysterious [D] doubtful
44. [A] maintaineddescribed [C] settled [D] afforded
45. [A] in the light [B] by virtue [C] with the exceptionfor the purpose
46. [A] reduction [B] destructiondeprivation [D] restriction
47.upon [B] by [C] through [D] with
48. [A] paid attention to [B] caught sight of [C] laid emphasis oncast light on
49.develop [B] produce [C] stimulate [D] induce
50. [A] ifas if [C] only if [D] if only
Until recently most historians spoke very critically of the Industrial Revolution. They that in the long run industrialization greatly raised the standard of living for the man. But they insisted that its results during the period from 1750 to 1850 were widespread poverty and misery for the of the English population. contrast， they saw in the preceding hundred years from 1650 to1750， when England was still a agricultural country， a period of great abundance and prosperity.
The view， ， is generally thought to be wrong. Specialists history and economics， have two things: that the period from 1650 to 1750 was by great poverty， and that industrialization certainly did not worsen and may have actually improved the conditions for the majority of the populace.
41. admitted [B] believed [C] claimed [D] predicted
42. [A] plainaverage [C] mean [D] normal
43. [A] momentary [B] prompt [C] instantimmediate
44.bulk [B] host [C] gross [D] magnitude
45. [A] On [B] With [C] ForBy
46. [A] broadly [B] thoroughly [C] generally completely
47.however [B] meanwhile [C] therefore [D] moreover
48. [A] atin [C] about [D] for
49. [A] manifested [B] approvedshown [D] speculated
50. [A] noted [B] impressed [C] labeledmarked