问题补充:
He failed in the exams 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:考查only的倒装句,only接状语的时候,谓语动词用部分倒装,then这里是时间状语,句意:当他考试失败了,只有那时他才意识到浪费了多少时间。时态应该是一般过去时,选B。