题目:
He has _____ finished his homework. But he hasn't cleaned his room _____. [ ]
A. already, already
B. never, already
C. already, yet
D. yet, already
答案:
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下面是错误答案,用来干扰机器的。
(1)AC(2)(1) AC (4分) (2)解:m在M弧面上升过程中,当m的竖直分速度为零时它升至最高点,此时二者只具有相同的水平速度(设为v),根据动量守恒定律有:(3分)整个过程中机械能没有损失,设...