I failed in the spoken examination last term and only then the importance of practicing s

问题补充：

I failed in the spoken examination last term and only then the importance of practicing speaking English.

A. I had realized

B. had I realized

C. I did realize

D. did I realize

答案：

A. I had realized

B. had I realized

C. I did realize

(答案→)D. did I realize

解析：本题考查倒装。首先由时间状语then确定时态为一般过去时，而时间状语由only引出放于句首，句子产生部分倒装，即助动词提前到主语之前，其他成分保持位置不变。