If $\;x-iy=\sqrt{\large\frac{a-ib}{c-id}}\;$ what is the value of $\;(x^{2}+y^{2})^{2}$?

Question

$(a)\;\large\frac{a^{2}+b^{2}}{c^{2}+d^{2}}\qquad(b)\;\large\frac{a^{2}+c^{2}}{b^{2}+d^{2}}\qquad(c)\;\large\frac{c^{2}+d^{2}}{a^{2}+b^{2}}\qquad(d)\;\large\frac{a^{2}+d^{2}}{c^{2}+b^{2}}$