A.x+y+1=0 B.x+y-1=0
C.x-y+1=0 D.x-y-1=0
答案:C x-y+1=0 x2+2x+y2=0化为(x+1)2+y2=1,
∴圆心(-1,0).
与直线x+y=0垂直的直线斜率为1,
∴所求的方程为y=x+1.