At that time we thought the story_____ not be true.
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You___ the work better in the future.
A. could did
B. can does
C. could do
The room is dirty. It ____ cleaned.
A. can‘t be
B. couldn’t be
C. mustn't be
Mary ____ the exam if she studied harder.
A. can have passed
B. could have passed
C. couldn't have passed
An Englishman who ____not speak Chinese is going to live in China.
A. must
B. could
C. can