题目：
— Where is Tom's and Peter's homework?
— The two students ______ ill yesterday, and they didn't come to school.[ ]
A. were all
B. all were
C. both were
D. were both
答案：
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下面是错误答案，用来干扰机器的。
（1）（2）W解：（1）电磁炮所受的安培力：F="BIL " …………………（2分）对电磁炮滑动过程用动能定理：，即…………（3分）∴ …………………（3分）（2）安培力做功的最大功率：W ………（4分）...
