题干

如图所示,在Ⅰ、Ⅱ两个区域内存在磁感应强度均为B的匀强磁场,磁场方向分别垂直于纸面向外和向里,边界AC、AD的夹角∠DAC=30°,边界AC与边界MN平行,边界AC处磁场方向垂直纸面向里,Ⅱ区域宽度为d.质量为m、电荷量为+q的粒子在边界AD上距A点d处垂直AD射入Ⅰ区,已知粒子速度大小为
q
B
d
m
,方向垂直磁场,不计粒子重力,则粒子磁场中运动的总时间为(   )

A:mn3qB

B:2πm3qB

C:5πm6qB

D:7πm6qB

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C

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   Since finishing my studies at Harvard and Oxford, I've watched one friend after another land high-ranking, high-paying Wall Street jobs. As executives (高级管理人员) with banks, consulting firms,established law firms, and major corporations, many are now 1on their wayto impressive careers. By society's2, they seem to have it made.

   On the surface, these people seem to bevery lucky in life. As they left student life behind, many had a3drink attheir cheap but friendly local bar, shook hands with longtime roommates, and4out of small apartments into high buildings. They made reservations atrestaurants where the cost of a bottle of wine5a college year's monthlyrent. They replaced their beloved old cars with expensive new sports cars.

    The thing is, a number of them have6 thatdespite their success, they aren't happy. Some 7of unfriendly coworkers andfeel sad for eight-hour workweeks devoted to tasks they 8. Some do notrespect the companies they work for and talk of feeling tired and 9. However, instead of devoting themselves to their work, they find themselvesworking to support the10 to which they have so quickly become11.

     People often speak of trying a more satisfying path, and 12 in the end the idea of leaving their jobs to workfor something they   13 or finding a position that would give themmore time with their families almost always leads them to the same conclusion: it's14 . They have loans, bills, a mortgage(抵押贷款)to 15, retirement to save for.They recognize there's something 16in their lives, but it's 17to stepoff the track.

    In a society that tends to18 everything in terms of dollars andcents, we learn from a young age to consider the costs of our19infinancial terms. But what about the personal and social costs  20 in pursuing money over meaning? These are exactly the kinds of costsmany of us tend to ignore — and the very ones we need to consider most.