问题补充:
So difficult it to work out the problem that I decided to ask Tom for advice.
A. I did find
B. did I find
C. I have found
D. have I found
答案:
A. I did find
(答案→)B. did I find
C. I have found
D. have I found
解析:句意:发现解决这个问题如此困难,所以我答应向汤姆咨询一下。So位于句首,应使用部分倒装。另外本句用过去时态。