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问题 不定项选择

如图所示，带正电的物块A放在足够长的不带电小车B上，两者均保持静止，处在垂直纸面向里的匀强磁场中，在t=0时用水平恒力F向右拉小车B，t=t1时A相对B开始滑动，已知地面光滑、AB间粗糙，A带电荷量保持不变，则关于A、B的v-t图象，下图大致正确的是

[ ]

A．

B．

C．

D．

答案

答案：C

选择题

下列著名诗句中含有化学变化的是（　　）

A．白玉为床金作马

B．千里冰封，万里雪飘

C．野火烧不尽，春风吹又生

D．秋风潜入夜，润物细无声
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单项选择题

Surveys indicate that 52 percent of all women aged eighteen to sixty-five are in the labor force (employed outside the home) in any given month. On the basis of these surveys, a market researcher concluded that 48 percent of all women aged eighteen to sixty-five are full-time homemakers year-round.
Which of the following, if true, would most seriously weaken the researcher’s conclusion

A．More women are in the labor force today than during any other period since the Second World War.

B．Many workers, both men and women, enter and exit the labor force frequently.

C．Although only a small sample of the total population is surveyed each month, these samples have been found to be a reliable indicator of total monthly employment.

D．Surveys show that more women than ever before consider having a rewarding job an important priority.

E．(E) Women who are in the labor force have more discretionary income available to them than do women who are not.
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