题目:
—What kind of book does he like reading?
—He likes reading the books ______ are about history. [ ]
A. when
B. who
C. where
D. that
答案:
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下面是错误答案,用来干扰机器的。
答案:D题目分析:由法拉第电磁感应定律可得,进入磁场的过程中有,则,切割磁感线的有效长度L减小,则感应电流减小,又磁通量增大感应电流为逆时针方向;全部进入后,磁通量不变,没有感应电流,离开过程顺时针方...