I failed in the 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：句意：上学期期末考试我没考及格，只在那时我才意识到学习的重要性。Only修饰状语then位于句首时需使用部分倒装，本句的时态应使用一般过去式。