2. 外语
  3. The normal human daily cycle of activity is some 7-8 hours’ sleep alternation with some 16-17 hours’ wakefulness and that the sl

The normal human daily cycle of activity is some 7-8 hours’ sleep alternation with some 16-17 hours’ wakefulness and that the sl

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问题     The normal human daily cycle of activity is some 7-8 hours’ sleep alternation with some 16-17 hours’ wakefulness and that the sleep normally coincides(1)_____ the hours of darkness. Our present concern is how easily and to what extent this(2)_____ can be modified.
    The question is not merely an academic one. The ease with which people can change from working in the day to working at night is a(3)_____ of growing importance in industry where automation (4)_____ round-the-clock working of machines. It normally(5)_____ from five days to one week for a person to adapt to a(6)_____ routine of sleep and wakefulness,(7)_____ during the day and working at night.(8)_____, it is often the case in industry that shifts are changed every week. This (9)_____ that no sooner has he got used to one routine(10)_____ he has to change to another, (11)_____ much of his time is spent neither working nor sleeping very(12)_____.
    One answer would seem to be(13)_____ periods on each shift, a month, or(14)_____ three months.(15)______, recent research has shown (16)_____ people on such systems will go back to their(17)_____ habits of sleep and wakefulness during the weekend and that this is quite enough to destroy any(18)_____ to night work built up during the week. The only real solution appears to be to(19)_____ the night shift to those permanent night workers whose(20)_____ may persist through all week-ends and holidays.
(2)
选项 A、cycle
B、period
C、circle
D、round
答案A
解析 由指示代词this可推断空格处的名词指代上一句的内容，上一句主要是讲“睡眠时间与清醒时间交替的情况”，四个选项中cycle“循环”复现首句的cycle，故为答案。period“时期”；circle“圆圈”：round“局”。
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