问题描述：
—How do you improve your listening,Mary?
—Just ______ listening to tapes,it's a good way,you know.
[ ]
A.to
B.in
C.by
D.for
—Just ______ listening to tapes,it's a good way,you know.
[ ]
A.to
B.in
C.by
D.for
问题解答：
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