题干
20．—Wow, you look good. Your hair looks fantastic. You’re such a wonderful friend. You’re so generous. I’ve always liked you.
—________! Get to the point. I haven’t got food all day.
A：Enough
B：Thank
C：Really
D：Rubbish
答案(点此获取答案解析）
A
的前n项和为Sn，若
等于（ ）
