He failed the midterm examination and only then how much time he had wasted.
A. he realized
B. did he realize
C. he had realized
D. had he realized
网友回答
A. he realized
(答案→)B. did he realize
C. he had realized
D. had he realized
解析：本题考查动词的时态和倒装句的用法。根据语法要求only引导状语位于句首时，需要使用倒装句结构。而该状语only then表明了动作发生在过去。