问题描述：
There are so many kinds of pens here.I can'tdecide______.
A.when to choose B.to choose which
C.which one to choose D.to choose which one
B和D哪个对?为什么?
A.when to choose B.to choose which
C.which one to choose D.to choose which one
B和D哪个对?为什么?
问题解答：
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