单选题 The secrets of sleep were a mystery for centuries simply because there was neither the means (51) them, nor the need. Only when candles gave way (52) gaslight, and gas to electricity, when man became able to (53) night into day, and double his output by working shifts round the clock, did people seriously start wondering (54) sleep could possibly be a waste of time. Our ability to switch night into day is very recent, and it is (55) if we will ever (56) want, or be able to give up our habit of (57) a good night's sleep. (58) , a remarkable research project in London has already discovered a few people who actually enjoy insomnia. Even chronic insomniacs often get hours more sleep. (59) they think. But, by placing electric contact (60) the eyes and on the head, it is possible to check their complaint by studying the tiny currents we generate which (61) the different brainwaves of sleep and (62) . This has shown that for some people seven or eight hours sleep a night are quite unnecessary.
(63) recent work has shown that (64) sleep is bad for you, so that if you are fortunate enough to be born with a body which needs only a small (65) of sleep, you may well be healthier and happier than someone who sleeps longer.