Let S = $\left\{ {\left( {x,y} \right) \in {R^2}:{{{y^2}} \over {1 + r}} - {{{x^2}} \over {1 - r}}} \right\};r \ne \pm 1.$ Then S represents :
an ellipse whose eccentricity is ${1 \over {\sqrt {r + 1} }},$ where r > 1
an ellipse whose eccentricity is ${2 \over {\sqrt {r + 1} }},$ where 0 < r < 1
an ellipse whose eccentricity is ${2 \over {\sqrt {r - 1} }},$ where 0 < r < 1
an ellipse whose eccentricity is $\sqrt {{2 \over {r + 1}}}$, where r > 1
