The value of $$\frac{\sin30^\circ-\cos60^\circ+\cot^2 45^\circ}{\cos30^\circ-\tan 45^\circ+\sin 90^\circ}$$ is equal to:

A

$$\frac{\sqrt{3}}{4}$$

B

$$\frac{2\sqrt{3}}{3}$$

C

$$\frac{\sqrt{3}}{2}$$

D

$$\frac{3}{2}$$