If $$\left(\frac{\tan \theta - \sec \theta + 1}{\tan \theta + \sec \theta - 1}\right) \sec \theta = \frac{1}{k}$$, then k = 

A

$$1 + \sin \theta$$

B

$$1 - \cos \theta$$

C

$$1 + \cos \theta$$

D

$$1 - \sin \theta$$