He failed the mid-term examination and only thenhow much time he had wasted.A. he realized

问题补充：

He failed the mid-term examination and only thenhow 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：句意：他期中考试不及格，只有到了那时，他才意识到他浪费了多少时间。

Only+副词/介词短语/状语从句等，后面的句子主体部分用倒装结构，即助动词+主语+动词原形，因此排除A,C。又根据句意，不是先意识到浪费时间了，然后考试不及格，故排除D。故选B。