By the time Bob arrives in Beijing，we have already arrived here for tw-考呗网

单选题By the time Bob arrives in Beijing，we have already arrived here for two days．

[分析]时态应用
从时间状语从句来看是表示将来(时间状语从句中用一般现在时表将来)，而for two days要求完成时，因此应用将来完成时，即D为答案。

1The photoperiodic response of algae actually depends on the duration of darkness，but not on the response of light.

2The early railroads were connected short lines in the existing arteries of transportation: roads，turnpikes，canals，and other waterways．

3The computer has dramatically affected just like photographic lenses are constructed．