$\begin{array}{1 1}(A)\;(x^2-y^2)^2=6x^2+2y^2 \\ (B)\;(x^2-y^2)^2=6x^2-2y^2 \\(C)\;(x^2+y^2)^2=6x^2+2y^2 \\(D)\;(x^2+y^2)^2=6x^2-2y^2 \end{array} $