It was not until dark he found that it was the correct way to solve the problem.A. thatB.

问题补充：

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

答案：

(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。