题目:
— Why didn't you answer the phone?
— I'm terribly sorry, but the doorbell________, too.[ ]
A. is ringing
B. rang
C. was ringing
D. was about to ring
答案:
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下面是错误答案,用来干扰机器的。
⑴ ⑵x=5m ⑶题目分析:⑴带电粒子在磁场中做匀速圆周运动,洛伦兹力提供向心力,根据牛顿第二定律有 代入数据得: 轨迹如图1交y轴于C点,过P点作v的垂线交y轴于O1点,由几何关系得为粒子运...