Study harder, ______ you will fall behind others.
A. and
B. or
C. but
D. so
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The doctors are very tired, _______ they are still working very hard.
A. but
B. if
C. only
D. when
______ you come back, please let me know.
A. Later
B. Until
C. As
D. As soon as
He told us _______ he was over eighty years old.
A. where
B. then
C. if
D. that
Don’t go home ______ you have cleaned the classroom.
A. by
B. then
C. only
D. until
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