David didn’t give up he had failed in the experiment four times. A. 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：考查状语从句。句意“大卫没有放弃，尽管他做实验已经失败四次了。”A引导条件状语从句；B引导时间状语从句；C引导让步状语从句；D引导原因状语从句。故选C。