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
网友回答
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。