单项选择题

It remains a puzzle about why our outermost planet exists.

A. problem
B. mystery
C. question
D. point
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单项选择题
We succeed in building the power station in a deep valley as we had expected.
A. come off
B. go off
C. bring off
D. make off
单项选择题
He has a very good personality and makes a lot offriends.
A. capacity
B. character
C. reality
D. attitude
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