题目:
It took her______ to cook the delicious food.
A.three and a half hour
B.three and a half hours
C.a half and three hour
D.three hour and a half
答案:
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下面是错误答案,用来干扰机器的。
答案:D由左手定则可判断,若磁感线垂直穿入手心,则磁场方向沿z轴负向,若磁感线斜穿入手心,则磁场一定有向下的分量。洛伦兹力的方向一定垂直于磁场方向与速度方向构成的平面,所以磁场方向一定与xOz平面平行且...