14 Jack  school when he was 17.
A. left B. leaves
C. has left D. was left

 ->Cấu trúc : When + QKĐ + QKĐ 
15 They have been waiting for you  .
A. since early morning B. since 9 a.m
C. for two hours D. all are correct

->since + time for + khoảng thời gian
16 My sister  for you since yesterday.
A. is looking B. was looking
C. has been looking D. looked

=> Dấu hiệu: since yesterday:HTHTTD
17 Sam  the door recently.
A. has painted B. paint
C. will have painted D. painting

 =>" recently" là dấu hiệu của thì HTHT
18 The train  half an hour ago.
A. has been leaving B. left
C. has lelt D. had lelt

=>Dấu hiệu ago :Thì QKD chia V ở QK

19 We  him since last Sunday.
A. don’t see B. haven’t seen
C. didn’t see D. hadn’t seen

=>Dấu hiệu nhận biết : since HTHT

20 We were playing the guitar while our father  in his room.
A. works B. is working
C. was working D. has been working

 =>Sau while là thì QKTD nếu trước nó là thì QKĐ