Find the mean proportional of $$(x + y)^{4}$$ and $$(x - y)^{4}$$

A

$$(x^{2} - y^{2})$$

B

$$(x^{2} - y^{2})^{2}$$

C

$$(x^{2} - y^{2})^{4}$$

D

$$(x^{2} - y^{2})^{3}$$