-- I have got a headache. -- No wonder. You_________ on the math exercises too long. 
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A
work
B
are working
C
have been working
D
worked
推荐题目
 It’s reported that in the past 50 years around 80 percent of Beijing’s courtyard houses ______.
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A
had wiped out
B
have wiped out 
C
have been wiped out 
D
had been wiped out
His uncle went abroad in 2010, and _______since.
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A
has not been heard of
B
had not been heard of
C
had not heard of
D
has not heard of
I have to see the doctor because I ________ a lot lately.
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A
have been coughing
B
had coughed
C
coughed
D
cough