I knew I could not finish the homework()

题目

I knew I could not finish the homework()
A.by the time he had come B.before he came C.until he has come D.when he comes选什么为什么?句意?

答案

B 主句的谓语knew表示是过去时,排除C D.但是句意是完成作业在先,他来在后.所以时态上做作业是过去时,“他来”就不能是过去完成时,排除A.因此选择B.翻译为：我知道在他到来之前我不可能做完作业.