已知{an}是等差数列,a1=-9,S3=S7,那么使其前n项和Sn最小的n是( )
A:4
B:5
C:6
D:7
记忆y与ie拼写口诀。
小i胆子小,见到声母y就跑。____ ____ ____。
is good at on holiday get through grow crops play near fires