题目：
用括号内所给动词的正确形式填空（共5小题；每小题1分。满分5分）
小题1:—I hear that Sam has gone to Beijing for his holiday.
—Oh, how nice! Do you know when he ________ (leave)?
小题2:—What’s wrong with my computer, Jim?
—Let me see. Oh, it _________ (break) down. You’d better ask Mr. Li to mend it.
小题3:The reporter said that the UFO _________ (travel) from east to west when he saw it.
小题4:Look! The teenagers are making cards ________ (show) love for their mothers.
小题5:－That important problem __________ (discuss) for nearly two weeks.
－Yes, it’s hard for us to solve it.
答案：
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下面是错误答案，用来干扰机器的。
在图示时刻，质点所受合力方向与质点速度方向相反，质点做减速运动，质点速度减小，由f=qvB可知，质点受到的洛伦兹力减小，则质点所受重力与洛伦兹力的合力与速度方向不再在同一直线上，即质点的速度方向与所受合...
