If $$f(x) = \frac{x}{\sqrt{1 - x^2}}$$ and $$g(x) = \frac{x}{\sqrt{1 + x^2}}$$ then $$(fog)x =$$

A

$$\sqrt{\frac{1 - x^2}{1 + x^2}}$$

B

$$\sqrt{\frac{1 + x^2}{1 - x^2}}$$

C

$$x^2$$

D

$$x$$