Giải các câu sau:
 
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14. We
(A) have studied (B) had studied (C) are going to study
15. We
all morning. Let's take a break now.
(D) were studying
the movie several times before Kevin got here.
(A) have watched
(B) are watching (C) had watched (D) will watch
16. Peter
(A) will stay
D17. After Bob
in Singapore since 2002.
(B) has stayed (C) stayed
his homework, he went to a movie with Cathy.
(D) was going to stay
(A) has done
(B) does
(C) had done (D) will do
18.A :
have Sam worked on solving the air pollution in his country? B : For about ten years.
(A) When
(B) While
(C) How often (D) How long
D19.While I
TV last night , Kelly
a shower
(A) watched ; took
(B) had watched ; had taken
(C) was watching ; was taking
20. When Sam got to the airport, he found the plane_ off'already.
(A) has taken (B) took
(D)have watched ; has taken
(C) is taking (D) had taken