问题
选择题
It was not until the teacher had explained it three times _______ how to work out the problem.
A．did he understand
B．had he understood
C．that he understood
D．that he didn’t understood
答案
答案：C
题目分析：考查固定句型。句义：直到老师解释了三次我才明白了怎样做这个题，首先给我关键词：It was …+that …,构成强调句型，根据倒装句：not until 位于句首构成：主到从不倒；用语强调句型不倒装，所以C正确。