Decide which of the choices given below would best complete the passage if inserted in the corresponding blanks. Mark the best choice for each blank on your answer sheet.ª¤
The normal human daily cycle of activity is of some 7-8 hours¡¯ sleep alternation with some 16-17 hours¡¯ wakefulness and that the sleep normally coincides(26) ____ the hours of darkness. Our present concern is with how easily and to what extent this(27)____ can be modified.ª¥
The question is no mere academic one. The ease with which people can change from working in the day to working at night is a(28)____ of growing importance in industry where automation(29)____ round-the-clock working of machines. It normally(30)____ from five days to one week for a person to adapt to aª©(31)____ªª routine of sleep and wakefulness, sleeping during the day and working at night. ª©(32)____,ªª it is often the case in industry that shifts are changed every week. This means that no sooner has he got used to one routine(33)____ he has to change to another, (34)____ much of his time is spent neither working nor sleeping very(35) ____.ª¥
One answer would seem to be(36)____ periods on each shift, a month, or even three months. (37)____, recent research has shown that people on such systems will revert to go back to their(38)____ habits of sleep and wakefulness during the week-end and that this is quite enough to destroy any(39)____ to night work built up during the week. The only real solution appears to be to hand over the night shift to those permanent night workers whose(40)____ may persist through all week-ends and holidays.

26.A.in          B.with          C.of          D.overª¤ª¤
27.A.cycle      B.period        C.circle      D.roundª¤ª¤ª¤
28.A.problem    B.difficulty    C.trouble      D.matterª¤ª¤
29.A.asks        B.invites        C.calls for    D.reacts toª¤
30.A.takes      B.spends        C.demands      D.asksª¤ 
31.A.former      B.returned      C.reversed    D.regularª¤ª¤
32.A.Therefore  B.Unfortunatelyª¤C.In a word    D.In comparisonª¤ª¤
33.A.as          B.when          C.then        D.thanª¤
34.A.though      B.so that        C.while        D.asª¤
35.A.efficiently B.good          C.easily      D.happilyª¤
36.A.shorter    B.better        C.longer      D.nicerª¤ª¤
37.A.So          B.In short      C.Similarly    D.Howeverª¤ª¤
38.A.new        B.normal        C.temporary    D.favouriteª¤ª¤
39.A.change      B.return        C.adaptation  D.tendencyª¤ª¤ª¤
40.A.wakefulness B.sleep          C.preference  D.habit