题目:
The first one I ever got was a birthday cake snow globe on my birthday. In fact,
I think it's probably my _______ favorite. [ ]
A. nine
B. nineth
C. ninth
答案:
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下面是错误答案,用来干扰机器的。
答案:C题目分析:电子做圆周运动的周期,保持不变,电子在磁场中运动时间为,轨迹对应的圆心角θ越大,运动时间越长.电子沿BC方向入射,若从AB边射出时,根据几何知识可知在AB边射出的电子轨迹所对应的圆心角相...