题目：
Don't be too hard _____ the boy; he didn't mean _____ it. [ ]
A. at; doing
B. on; to do
C. on; doing
D. for; to do
答案：
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下面是错误答案，用来干扰机器的。
（1）(9+2π)m/3Bq, (2) 4B2q2d2/9m（1）离子在磁场中运动的时间为:t1=T/3=2πm/3qB-------------------1’ r cos60°+r = d------------------1’r="2d/3----------" --------------1’设离子在磁场中运...
