如图所示，在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强_爱下问搜题

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问题选择题

如图所示，在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场，一个不计重力的带电粒子从坐标原点O处以速度v进入磁场，粒子进人磁场时的速度方向垂直于磁场且与x轴正方向成120°角，若粒子穿过y轴正半轴后在磁场中到x轴的最大距离为a，则该粒子的比荷和所带电荷的正负是（　　）

A．，正电荷

B．，正电荷

C．，负电荷

D．，负电荷

答案

答案：C

完形填空

A teacher once told each of her students to bring a clean plastic bag and a bag of potatoes to school. For every person they didn’t want to forgive(原谅) in their lives, they chose a potato, wrote the person’s 1 and the date on it and put it in the plastic bag. Some of their bags were very 2 . They were then told to carry this bag with them 3 for one week. They would put it beside their bed at night, on the seat when sitting in a car or on a bus , and next to their desks at 4 . The 5 carrying the bag around with them made students get to know what a weight they were carrying in their minds. They had to pay attention to(注意) it all the time so that they wouldn’t 6 it or leave it in embarrassing(尴尬的) places. As time passed by, the potatoes went 7 and smelt terrible. Too often we think of tolerance(宽容) as a 8 to other people, but it clearly is for 9 ! If we choose to keep our sadness and hatred(仇恨) in our hearts, we will have to 10 them around all our lives.

问答题

简述课外活动的意义。