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
网友回答
D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。