549.Pleasant music is often played ______ classes to make students refreshed and relaxed for a while.
A.between
B.among
C.over
D.after
550.Although _______ my opinion,the old professor didn't come up with his own.
A.against
B.on
C.for
D.in
549.答案是A;between用于两者之间，也可指多个事物每两者之间；among用于三者或三者以上。课间是指两节课之间，故选A。
550.答案是A;against one'e opinion反对某人的见解；for one's opinion 同意某人的见解；in one's opinion 在某人看来。
