If $$\sin 23^\circ = \frac{a}{b}$$, then the value of $$\sec 23^\circ - \sin 67^\circ$$ is________________

A

$$\frac{a^2}{\sqrt{b^2 - a^2}}$$

B

$$\frac{b^2 - a^2}{ab}$$

C

$$\frac{a^2}{b \sqrt{b^2 + a^2}}$$

D

$$\frac{a^2}{b \sqrt{b^2 - a^2}}$$