If $$a = \frac{\sqrt{3} - 1}{\sqrt{3} + 1}$$ and $$b = \frac{\sqrt{3} + 1}{\sqrt{3} - 1}$$ then the value of $$\frac{a^2 - ab + b^2}{a^2 + ab + b^2}$$ is

A

$$\frac{5}{4}$$

B

$$\frac{13}{15}$$

C

$$\frac{13}{14}$$

D

$$\frac{4}{5}$$