问题
单项选择题
We have kept（）our friendship by writing to each other, so we are true friends.
A.back
B.up
C.off
D.down
答案
参考答案：B
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We have kept（）our friendship by writing to each other, so we are true friends.
A.back
B.up
C.off
D.down
参考答案：B
