In completely factored form

$\displaystyle a^2x^2-b^2y^2+b^2x^2-a^2y^2$

is.......

a) $\displaystyle (a-b)(a+b)(x^2+y^2)$

b) $\displaystyle (a^2+b^2)(x^2-y^2)$

c) $\displaystyle (a^2-b^2)(x^2+y^2)$

d) $\displaystyle (a+b)(x-y)$

e) $\displaystyle (a^2+b^2)(x+y)(x-y)$

what would be the answer?

HELP!!