$\sec\;h^{-1} (\sin \theta)$ is equal to

Question

\[\begin {array} {1 1} (a)\;\log \tan \frac{\theta}{2} & \quad (b)\;\log \sin \frac{\theta}{2} \\ (c)\;\log \cos \frac{\theta}{2} & \quad (d)\;\log \cot \frac{\theta}{2} \end {array}\]