It was not until dark he found he thought was the correct way to solve the problem.A.

问题补充：

It was not until dark he found he thought was the correct way to solve the problem.

A. that; what

B. that; that

C. when; what

D. when; that

答案：

(答案→)A. that; what

B. that; that

C. when; what

D. when; that

解析：这是—个带有宾语从句的强调句型。主句是not...until句型。该句型被强调时，只能强调not+until引导的状语。宾语从句是由关系代词what引导的。