问题
选择题
Not until they left school ______ how much their teachers loved them and helped them.
A．they realized
B．had they realized
C．they would realize
D．did they realize
答案
答案：D
本题考查倒装结构。Not until放在句首，主句要发生主谓倒装，再根据时态，“他们意识到”是在“他们离开学校之后”，故用一般过去时。故选D。