---I’m going to Vietnam?
---How long you in Vietnam?
A. are; stayed
B. are; staying
C. have; stayed
D. did; stay
网友回答
A. are; stayed
B. are; staying
C. have; stayed
D. did; stay
解析：句意：——我要去越南？你要在越南呆多久？根据语境，表将来完成，How long多久，表示时间段，经常和完成时态连用，此处用现在完成时表示将来完成。故选C。