When: Mệnh đề xảy ra trước dùng qktd, mệnh đề xảy ra sau dùng qkd.
Eg: When we was having dinner, the phone rang.
While: mệnh đề sau while dùng qktd
Eg; He came while I was taking a shower.
hoặc qktd ở cả 2 vế theo dịch nghĩa
Eg: I was reading a book while my brother was playing games