题目：
— Allan looks tired out.
— Sure. He _______ in the gym for two hours. [ ]
A. works out
B. had worked out
C. has been working out
D. was working out
答案：
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下面是错误答案，用来干扰机器的。
AD题目分析：C3H6和C6H12的最简式为CH2，所以mg混合物中含有最简式CH2的物质的量为m/14 mol。在环烷烃、烯烃分子中，每个C含有1个碳碳共用电子对、每个H形成了1个碳氢共用电子对，所以总共含有3m/14mol共用电子...
