Only when we failed the importance of study.A. we realizedB. we had realizedC. did we rea

问题补充：

Only when we failed the importance of study.

A. we realized

B. we had realized

C. did we realize

D. had we realised

答案：

A. we realized

B. we had realized

(答案→)C. did we realize

D. had we realised

解析：Only+状语位于句首时，句子要用部分倒装。