If $\tan \theta_1 = k \cot \theta_2$, then $\frac{\cos (\theta_1 - \theta_2)}{\cos (\theta_1 + \theta_2)}$ is equal to :

Question

( A ) $\frac{1-k}{1+k}$
( B ) $\frac{1+k}{1-k}$
( C ) $\frac{k+1}{k-1}$
( D ) $\frac{k-1}{k+1}$