矿井总回风巷或一翼回风巷中瓦斯或二氧化碳浓度超过（）时，必须立即查明原因，进行处理。

Taking a Nap During the Day
Medical experts say most Americans do not get enough sleep. They say more Americans need to rest for a short period in the middle of the day.       continuing with other activities.
One study earlier this year found that persons who     for a few minutes during the day were less likely to die of heart disease. The study       more than 2,300 Greek adults for about six years. Adults who rested for half an hour at least three times a week had a 37 percent       risk of dying from heart disease than those who did not nap.
The study organizers said the strongest evidence was in working men. They said naps might improve      by mitigating(减低) tension caused by work.
Some European and Latin American businesses have supported the       of napping for many years. They urge people to      __ 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        and accidents, and       _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        important duties when they feel sleepy. And they say the best thing to do is to take a nap. About twenty minutes of rest is all you need. Experts say this provides extra energy and can increase your effectiveness       _ the end of the day. But experts     _that a nap should last no more than twenty to thirty minutes. A longer nap will put the body into deep sleep and waking up will be difficult.

小题1:	A．as B．when C．before D．after

小题2:	A．laugh B．sleep C．walk D．move

小题3:	A．knew B．learned C．studied D．followed

小题4:	A．less B．more C．lower D．higher

小题5:	A．life B．health C．thinking D．ability

小题6:	A．way B．idea C．suggestion D．experiment

小题7:	A．leave B．repeat C．change D．improve

小题8:	A．work B．time C．energy D．mistakes

小题9:	A．too B．also C．never D．seldom

小题10:

A．make B．bring C．carry out D．create

小题11:

A．until B．while C．unless D．during

小题12:

A．say B．think C．guess D．warn