[单项选择]We all know that the normal human daily cycle of activity is some 7—8 hours’ sleep alternating with some 16—17 hours’ wakefulness and that, broadly speaking, the sleep normally coincides with the hours of darkness. Our present concern is how easily and to what extent this cycle can be modified.
The question is no more academic one. The ease, for example, with which people can change from working in the day to working at night, is a question of growing importance in industries 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 and wakefulness, sleeping during the day and working at night. Unfortunately, it is often the case in industries where 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 soon. This means that no sooner has he got used to one routine than he has to
A. Body temperature may serve as an indication of a worker’s performance.
B. Taking body temperature at regular intervals can show how quickly a person adapts to the changes of routine.
C. The selection of a number of permanent night shift workers has proved to be the best solution to problems of the round-the-clock working system.
D. Disturbed sleep occurs less frequently among those on permanent night or day shifts.