We all know that the normal human daily cycle 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 win how easily and to what extent this cycle can be modified. One answer would seem to be longer periods on each shift, a month, or even three months. Recent research by Bonjer of the Netherlands, however, has shows that people on such systems will revert to their normal habits of sleep and wakefulness during the week-end and that this is quite enough to destroy any adaptation to night work built up during the week. 1. The question raised in Paragraph 1 is no mere academic one B)because sleep normally coincides with the hours of darkness. D)because shift work in industry requires people to change the sleeping habits. A) people hate the inconvenience of working on night shifts. C) not all industries work at the same hours. 3. According to the passage, the best solution on the problem seems to be B) to make periods on each shift longer. D) to find ways of selecting people who adapt quickly. A) the third week C) a third of the time 5. In the last sentence of the second paragraph, another means B) another shift D) another person