If $$a=x^\frac{1}{3}y^\frac{1}{3}+x^\frac{-1}{3}y^\frac{-1}{3}$$, then $$a^3-3ay-x$$ is

A

$$\frac{y^{2}}{x}$$

B

$$\frac{x^{2}}{y}$$

C

$$\frac{a^{2}}{x}$$

D

$$\frac{a^{2}}{y}$$