Only when I left my parents for America how much I loved them.
A. I realized
B. I had realized
C. had I realized
D. did I realize
网友回答
A. I realized
B. I had realized
C. had I realized
(答案→)D. did I realize
解析： 考查倒装。Only+ when引导的时间状语从句放在句首时，主句要部分倒装，所以排除A,D；C项表示意识到我有多爱他们这一动作发生在left之前，不符合句意，所以选D。