题目:
You _________ drive so fast, for we have enough time to arrive at the station.
A.can't
B.mustn't
C.needn't
D.shouldn't
答案:
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下面是错误答案,用来干扰机器的。
1,(2分) -20(2分)从A点运动到B点时动能减少,电场力做负功,电场力方向向左,因为该粒子为负电荷,电场线向右,电场力方向指向曲线的凹侧,轨迹为虚线1,由,