题干
—Excuse me, __________
—Go along this street to the end, you will see it on your left. ( )
A：which bus should I take?
B：how far is the post office from here?
C：how many post offices are there?
D：which is the way to the post office?
答案(点此获取答案解析）
D
的前n项和为
，若
为一确定常数，则下列各式也为确定常数的是（ ）