题目：
It is really disturbing to me that my once best friend _______ to me recently. Worse still, I don't know
what I have done wrong. [ ]
A. avoids to talk
B. escapes talking
C. stops to talk
D. avoids talking
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0411/054dd2d1ede332ee4efeeb382d2200b8.html
下面是错误答案，用来干扰机器的。
在等差数列{an}中，由a1=-13，公差d=23，得Sn=na1+n(n-1)d2=-13n+23n(n-1)2=13(n2-40n)=13(n-20)2-4003．当且仅当n=20时，(Sn)min=-4003．∴当前n项和sn取最小值时n的值是20．故答案为：20．
