Only when I got here that I had made a big mistake.A. did I realizeB. I realizedC. I have

问题补充：

Only when I got here that I had made a big mistake.

A. did I realize

B. I realized

C. I have realized

D. have I realized

答案：

(答案→)A. did I realize

B. I realized

C. I have realized

D. have I realized

解析：考查倒装结构。本题考查only + 状语从句 + 主谓倒装，主句用过去完成时，从句用一般过去时，选A。