If $|x| = x$, then $\frac{1}{2} \log \begin{pmatrix} \frac{1+x}{1-x} \end{pmatrix}$ is equal to :

Question

( A ) $\sin^{-1}x$
( B ) $\cos^{-1}x$
( C ) $\tan^{-1}x$
( D ) $\tan^{-1}x$