【题目】________ the parents had read his letter ________ the true state of affairs.
A. It was until… that they understood
B. It was not until… they understood
C. Until… did not they understand
D. Not until… did they understand
在线课程【答案】D
【解析】
试题分析：考查倒装句。句意：直到他的父母亲读了他的信才知道事情的真实状态。Not until引导的时间状语从句放在句首，主句倒装。故可知选D项。