It was not until dark he found that it was the correct way to solve the problem.
A. that
B. what
C. which
D. when
网友回答
(答案→)A. that
B. what
C. which
D. when
解析：这是强调句型其结构是It was+被强调部分+ that+其他，判断强调句型的方法是把It was that去掉整个句子不缺成分，是成立的。当被被强调部分是until+状语时，应把句中的not与until+状语一起放在被强调部分。故选A。