It’s snowing heavily outside. Put on your coat,_________ ,you’ll catch a cold.
#55237
A
and
B
or
C
though
D
but
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Students should _______ to smoke.   
#58541
A
not be allowed
B
be not allowed
C
not allow
D
be allowed
He met many problems ______ he was going over his lessons.
#58104
A
before
B
as soon as
C
since
D
while