Keep quiet _____ you have finished your assignment.
A. as
B. while
C. when
D. after
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_____ you know the answer, you’ll find it fairly easy.
A. Unless
B. While
C. Once
D. Though
We had no sooner arrived at the airport _____ it was time to check in.
A. than
B. when
C. then
D. before
We must try our best to get good marks _____ we may win the first prize.
A. as
B. therefore
C. if
D. in order that
It is a long time _____.
A. since I last saw you
B. ago I last saw you
C. when I last saw you
D. then I last saw you