Not until they left school how much their teachers loved them and helped them.
A. they realized
B. did they realize
C. had they realized
D. they would realize
网友回答
A. they realized
(答案→)B. did they realize
C. had they realized
D. they would realize
解析：考查倒装句和时态：句意：直到我们离开学校我们才意识到老师是多么爱我们并且帮助我们。Not until引导的时间状语从句放在句首，主句用部分倒装，因为hi在离开学校后才意识到，所以用一般过去时，选B。