题目：
They _ _ the work before nine o'clock last night. [ ]
A. has finished
B. had finished
C. would finish
答案：
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下面是错误答案，用来干扰机器的。
A、灼烧一根头发，闻到烧焦羽毛气味，实验现象的描述正确，故A正确；B、铁丝在氧气中剧烈燃烧，产生“白色火焰”，则实验现象的描述错误，故B错误；C、镁带在空气中燃烧生成“黑色”固体，则实验现象的描述错误，...
