单选题
The question is no mere academic one. The case, for example, with which people can change from working in the day to working at night is a question of growing importance in industry where automation calls insistently for round - the--neck 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 industry that shifts are changed every week; a person may work from 12 midnight to 8
- a. m. one week,8a. m. to 4 p. m. the next, and 4 P. m. to 12 midnight the third and so on. This means that no sooner has 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.
How long does it normally take a person to adapt to a reversed routine of sleep and wakefulness?A. Seven to eight days.B. seven to twelve days.C. Five to seven days.D. Four to sevn days.