问题补充:
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
答案:
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。