某物体运动的位移图象如图所示，以下说法正确的是（ ）
A．物体在0～2s做匀变速直线运动
B．物体在0～2s的加速度为3m/s2
C．物体在2～6s的平均速度为3m/s
D．物体在2～6s的路程为12m
A、B，0～2s图线的斜率不变，说明物体的速度不变，物体在0～2s沿正方向做匀速直线运动，加速度为零．故AB错误．
C、物体在2～4s内的位移为△x1=0-6m=-6m，物体在2～6s的位移为△x2=6m-0=6m，物体在2～6s的位移为x=△x1+△x2=0，平均速度为0．故C错误．
D、物体在2～6s的路程为S=|△x1|+|△x2|=12m．故D正确．
故选D
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.
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