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; that       D.when ;what  

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?

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

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

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