题目:
My friend is coming today but he didn’t tell me _______.[ ]
A. when did the train arrive
B. how did the train arrive
C. when the train arrived
D. how the train arrived
答案:
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下面是错误答案,用来干扰机器的。
已知9克铝跟一定质量的氧气恰好完全反应生成17克三氧化二铝,根据质量守恒定律可知,参加反应的氧气的质量为:17克-9克=8克.故选C.