Part B (10 points)
You are going to read a list of headings and a text about human daily cycle of activity. Choose the most suitable heading from the list for each numbered paragraph. The first and last paragraphs of the text are not numbered. There is one extra heading which you do not need to use.
(41) We all know that normal human daily cycle of activity is of 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 with how easily and to what extent this normality can be modified.
(42) The question is no more an 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-clock working of machine. 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, 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 has he got used to one routine than he was to change to another, so that much of his time is spent neither working or sleeping efficiently.
(43) One answer would seem to be longer periods on each shift, a month, or even three months. Recent research, however, has shown that people on such systems will get back into their normal habits of sleep and wakefulness during the weekend and that this is quite enough to harm any adaptation to night work built up during the week.
(44) The only real solution appears to be to hand over the night shift to a gang of permanent night workers whose adaptation to night work may persist through all weekends and holidays. An interesting study of the domestic life and health of night shift workers was carried out by Brown in 1967. She found a high incidence of disturbed sleep, digestive disorder and domestic disruption among those on alternating day and night shifts, but no abnormal occurrence of these symptoms among those on permanent night work.
(45) This latter system then appears to be the best long term policy, but, for the time being, 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.

A. Normality is difficult to be modified especially in industry
B. The only real solution
C. The normal human daily cycle
D. Weekends add the difficulty to adaptation to sleep and wakefulness
E. The present work to be done
F. To work on weekends can help the adaptation