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

问题描述:

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?

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