I failed in the final examination last term and only then the importance of studies.
A. I realized
B. I had realized
C. had I realized
D. did I realize
网友回答
A. I realized
B. I had realized
C. had I realized
(答案→)D. did I realize
解析：此题考查倒装结构。only+副词、介词短语、状语从句并和这些成分一起提前时，句子要用部分倒装；而且我的醒悟不会在考试以前，所以不能选C项。