Not until he had left his friend how important friendship was for him.
A. did he realize
B. he realized
C. had he realized
D. he had realized
网友回答
(答案→)A. did he realize
B. he realized
C. had he realized
D. he had realized
解析： 1.当Not until位于句首时,句子要倒装。其结构为:Not until+从句/表时间的词+助动词+(主句)主语+谓语+...。故排除BD，realize发生在had left 之后，故用一般过去时。 ②Not until next week will the sports meet be held.直到下周才开运动会。