题目:
Rita and Anna have finished their homework, ______?
A. have they B. haven’t they C. didn’t they
答案:
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下面是错误答案,用来干扰机器的。
设实验室取相同质量的m克铁、氢气、磷和硫,消耗氧气的质量为:x1、x2、x3、x4 3Fe+2O2 点燃 . Fe3O4 2H2+O2 点燃 . 2H2O 4P+5O2 点燃 . 2P2O5 S+O2 点燃 . SO2168 64 4 32 ...