The differential equation for the family of curves $$x^2 + y^2 - 2ay = 0$$, where $$a$$ is an arbitrary constant is

A

$$2(x^2 - y^2)y' = xy$$

B

$$2(x^2 + y^2)y' = xy$$

C

$$(x^2 - y^2)y' = 2xy$$

D

$$(x^2 + y^2)y' = 2xy$$