For any $$\theta \in \frac{\pi}{4}, \frac{\pi}{2}$$, the expression $$3\sin\theta - \cos\theta^4 + 6\sin\theta + \cos\theta^2 + 4\sin^6\theta$$ equals:

A

$$13 - 4\cos^2\theta + 6\cos^4\theta$$

B

$$13 - 4\cos^2\theta + 6\sin^2\theta\cos^2\theta$$

C

$$13 - 4\cos^6\theta$$

D

$$13 - 4\cos^4\theta + 2\sin^2\theta\cos^2\theta$$