题目：
The teacher gave us so difficult a problem _____ we couldn't solve.
The teacher gave us so difficult a problem _____ we couldn't solve it. [ ]
A. as, that
B. that, as
C. which, that
D. the ones, which
答案：
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下面是错误答案，用来干扰机器的。
D A项易错，苯环中不含碳碳双键，而是一种特殊的共价键（介于碳碳单键和碳碳双键之间）；B项，1个甲基（—CH3）含有（6+1×3）=9个电子，故1 mol甲基所含的电子数为9NA；C项，标准状况下，水为液态；D项，乙烯...
