Question

【题目】David didn't give up he had failed in the experiment four times.
A.if
B.while
C.though
D.since

Answer 1

【答案】C
【解析】考察介词辨析，句意：David 没有放弃，尽管他的实验已经失败了四次，A如果，B当……，C尽管，D自从……，故选C。