By the time you arrived in London, we () in Europe for two weeks.

题目

By the time you arrived in London, we () in Europe for two weeks.
A. have stayed
B. will have stayed.
为什么选B?从句为什么用过去时,而主句用将来时?

答案

选B,虚拟语气,主句可以用将来完成时,当然用would have stayed更好.