A:①③
B:②④
C:①④
D:②③
____
根据下面图片以第一人称写一篇短文,词数80左右。开头已给出 I took part in a friend's birthday party in the evening. It rained when I went home. On my way back home.
等差数列{an}中,a3=6,a8=16,Sn是数列{an}的前n项和,若Tn=1S1+1S2+...+1Sn,则52T9最接近的整数是 ( )
如图,抛物线y=ax2+bx+c(a、b、c为常数,a≠0)经过点A(﹣1,0),B(5,﹣6),C(6,0).