单项选择题

Taking a Nap During the Day
Medical experts say most Americans do not get (51) sleep. They say more Americans need to rest for a short period in the middle of the day. They are advising people to sleep lightly before (52) with other activities.
One study earlier this year found that persons who sleep for a few minutes during the day were less (53) to die of heart disease. The study followed more than 2, 300 Greek adults (54) about six years. Adults who rested for half an hour (55) three times a week had a 37 present lower risk of dying from heart disease than those who did not nap.
Study organizers said the strongest evidence was in working men. They said naps might improve (56) by mitigating tension caused by work.
Some European and Latin American businesses have supported the (57) of napping for many years. They urge people to (58) work, go home and have a nap before returning. In the United States, some companies let workers rest briefly in their offices. They believe this reduces (59) and accidents, and (60) increases the amount of work a person can do.
Sleep experts say it is likely that people make more mistakes at work than at other times. They say people should not carry out important duties when they feel (61) And they say the best thing to do is to take a nap. About twenty minutes of rest is (62) you need. Experts say this provides extra energy and can increase your effectiveness (63) the end of the day. But experts warn that a nap (64) last no more than twenty to thirty minutes. A longer nap will put the body into deep sleep and waking up will be (65) .