If $$\cos^4 \alpha - \sin^4 \alpha = \frac{5}{6}$$, then the value of $$2 \cos^2 \alpha - 1 = ----------$$

A

$$\frac{11}{6}$$

B

$$\frac{5}{6}$$

C

$$\frac{6}{11}$$

D

$$\frac{6}{5}$$