David didn’t give up he had failed in the experiment four timesA. ifB. whileC. thoughD.

问题补充：

David didn’t give up he had failed in the experiment four times．

A. if

B. while

C. though

D. since

答案：

A. if

B. while

(答案→)C. though

D. since

解析：此题考查连词，though引导让步状语从句，表示尽管。