In order to find the missing child, villagers _______ all they can over the past five hours.
#100499
A
did
B
do
C
had done
D
have been doing
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The construction of the two new railway lines   by now.
#99633
A
have been completed
B
has been completed
C
has coompleted
D
have completed
I am so tired,for I ________ English for 2 hours.
#99761
A
is studying 
B
have been studying
C
was studying 
D
had been studying