By the time you arrive in London, we in Europe for two weeks.
A. shall stay
B. have stayed
C. will have stayed
D. have been staying
网友回答
A. shall stay
B. have stayed
(答案→)C. will have stayed
D. have been staying
解析：by the time引导的时间状语从句中使用了一般现在时表将来，主句应用将来时，因此排除B 、D。句意：当你到达伦敦时，我们将已经在欧洲逗留两周了。由此判断应用将来完成时表示将来某一时间或动作发生之前已经完成的动作。故选C。