They kept trying they must have known it was hopeless.
A. if
B. because
C. when
D. where
网友回答
A. if
B. because
(答案→)C. when
D. where
解析：when在此的意思不是“当……的时候”，而是“尽管”、“虽然”的意思。又如：He walks when he might take a taxi.尽管他可以坐出租车，但他却走路。He stopped trying when he might have succeeded next time.尽管他本来下次就可以成功的了，但他却停止努力了。
【标签】熟词生义