- _________are his football clothes?
- Under the bed.
A:Where
B:Who
C:Whose
D:What
歌曲《松花江上》唱出东北人民流离失所、家破人亡的悲痛之情,它创作的背景是( )
已知等差数列{an}的前n项和为Sn,且a1=1,S3=0.