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  3. We all know that the normal human daily cycle of activity is of some 7-8 hours’ sleep alternating with some 16-17 hours’ wakefu

We all know that the normal human daily cycle of activity is of some 7-8 hours’ sleep alternating with some 16-17 hours’ wakefu

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问题     We all know that the normal human daily cycle of activity is of some 7-8 hours’ sleep alternating  with some 16-17 hours’ wakefulness and that, broadly s peaking, the sleep normally coincides with the hours of darkness. Our present concern is with how easily and to what extent this cycle can he modified.
    The question is no mere academic one. The ease, for example, with which people can change from working in the day to winking at night is a question of growing importance in industry where automation  calls for round-the-clock working of machines. It normally takes from five days to one week for a person to adapt to a reversed routine of sleep end wakefulness, sleeping during the day end working at night. Unfortunately, it is often the case in industry that shifts are changed every week; a person may work from 12 midnight to 8 a.m. one week, 8 a.m. to 4 p.m. the next, and 4 p. m. to 12 midnight the third and so on. This means that no sooner bas he got used to one routine than he has to change to another, so that much of his time is spent neither working nor sleeping very efficiently.
    The only real solution appears to be to hand over the night shift to a number of permanent night workers. An interesting study of the domestic life and health of night-shift workers was carried out by Brown in 1957. She found a high incidence of disturbed sleep and other disorders among those on alternating day and night shifts, but no abnormal occurrence of these phenomena among those on permanent night work.
    This latter system then appears to be the best long-term policy, but meanwhile something may be done to relieve the strains of alternate day and night work by selecting those people who can adapt most quickly to the changes of routine. One way of’ knowing when a person has adapted is by measuring  his body temperature. People engaged in normal daytime work will have a high temperature during the hours of wakefulness and a low one at night; when they change to night work the pattern will only gradually go back to match the new routine and the speed with which it does so parallels, broadly speaking, the adaptation of the body as a whole, particularly in terms of performance. There from, by taking body temperature at intervals of two hours throughout the period of wakefulness it can be seen how quickly a person can adapt to a reversed routine, and this could be used as a basis for selection. So far, however, such a form of selection does not seem to have been applied in practice.
The main problem of the round-the-clock working system lies in______.
选项 A、the inconveniences brought about to the workers by the introduction of automation
B、the disturbance of the daily life cycle of workers who have to change shifts too frequently
C、the fact that people working at night are often less effective
D、the fact that it is difficult to find a number of good night workers
答案B
解析 文中第二段指出工人们适应新的工作时间通常要5至7天，但shifts are changed every week，这就导致了workers spent neither working nor sleeping very efficiently，选项 B符合。
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