Only when I made it to the train station that I had left my ticket at home.A. have I real

问题补充：

Only when I made it to the train station that I had left my ticket at home.

A. have I realized

B. did I realize

C. had I realized

D. would I realize

答案：

A. have I realized

(答案→)B. did I realize

C. had I realized

D. would I realize

解析：考查倒装句。Only +状语放在句首，使用部分倒装。从句不倒装，主句倒装。此题是Only+时间状语放在句首，根据时态应选B。