For $$0 < a < 1$$, the value of the integral $$\int_0^{\pi} \frac{dx}{1 - 2a\cos x + a^2}$$ is :

A

$$\frac{\pi^2}{\pi + a^2}$$

B

$$\frac{\pi^2}{\pi - a^2}$$

C

$$\frac{\pi}{1 - a^2}$$

D

$$\frac{\pi}{1 + a^2}$$