B) $$\frac{x}{x+y} + \frac{y}{x-y}$$;

в) $$\frac{x}{x+y} + \frac{y}{x-y} = \frac{x(x-y) + y(x+y)}{(x+y)(x-y)} = \frac{x^2 - xy + xy + y^2}{x^2 - y^2} = \frac{x^2 + y^2}{x^2 - y^2}$$;

Ответ: $$\frac{x^2 + y^2}{x^2 - y^2}$$