The correct option is A x+y=0
Axis of a parabola is the line about which it is symmetric. Hence, for axis of a parabola, put the quadratic (square) term equal to zero.
x2+2xy+y2−5x+5y−5=0
⇒(x+y)2−5(x−y)−5=0
Therefore, equation of the axis of the parabola is x+y=0