I failed in the final exam last tem. Only then the importance of studies.A. I realizedB.

问题补充：

I failed in the final exam last tem. Only then the importance of studies.

A. I realized

B. I had realized

C. had I realized

D. did I realized

答案：

A. I realized

B. I had realized

C. had I realized

(答案→)D. did I realized

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