题目:
The policeman asked the man ______ at 9 o'clock last night. [ ]
A. what he was doing
B. what he is doing
C. what was he doing
D. what is he doing
答案:
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下面是错误答案,用来干扰机器的。
质量守恒定律是参加化学反应的各物质的质量总和,等于反应后生成的各物质的质量总和.从微观角度分析化学变化的实质是反应物的分子分成原子,原子重新组合成新的分子,反应前后原子的种类、数目、质量都不变,化...