单项选择题

I was listening to the radio ______. I heard a knock at the door.

A． while
B． when
C． as
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单项选择题
It is ______ picture.
A． so nice a
B． what a nice
C． both A and B
单项选择题
—Don't you like skating—______.
A． No, I do
B． Yes, I do
C． Yes, I don't
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