题目

题型：不详难度：来源：

Only after spending several nights working on the math problem         to wonder whether the problem was wrongly set.

A．had he begun

B．he began

C．did he begin

D．began he

答案

C

解析

only+状语位于句首要采用倒装，又因为叙述过去的事情所以用一般过去时态。句意：只有在花费数晚上的时间计算这道题之后他才怀疑是否问题出错了。