Given -- the equations of the two asymptotes of the hyperbola are $x+y=0$ and $x-y=0$, then its eccentricity is ( )
(A) $\frac{\sqrt{2}}{2}$
(B) $\sqrt{2}$
(C) $2 \sqrt{2}$
(D) $\sqrt{2}+1$
5. (B).

The equation of the hyperbola has the form $x^{2}-y^{2}=k$.