They kept trying they must have known it was hopeless.? A. if B. because? C. whe

They kept trying _____ they must have known it was hopeless.?

A. if B. because?　 C. when　 D. where

试题答案

C

when在此的意思不是“当……的时候”，而是“尽管”、“虽然”的意思。