…

a 2009+a 20 10+a 20 1 1+a 20 12 =(0-20 10+0+20 12)= 2，

s 20 12 = a 1+a2+a3+a4+…+a 20 12

=(0-2+0+4)+(0-6+0+8)+…+(0-20 10+0+20 12)

=2×503= 1006

So choose one