Chọn đáp án đúng

1.Modern transportation can speed a doctor (A)to the side of a (B)sick person, (C)even if the patient lives on an (D)isolated farm.
2.As long as they....... for more than three days, they can sleep at my flat A. don't stay B.haven't stay C.aren't staying D.wouldn't stay
Giải thích rõ giúp mình với, mình tìm mấy trang khác nhưng giải thích khó hiểu quá