If $\;z_{1} ,z_{2}\;$ and $\;z_{3} ,z_{4}\;$ are 2 pairs of conjugate numbers , then $\;arg(\large\frac{z_{1}}{z_{4}}) + arg(\large\frac{z_{2}}{z_{3}})\;$ equals :

Question

$(a)\;\normalsize 0\qquad(b)\;\large\frac{\pi}{2} \qquad(c)\;\large\frac{3\pi}{2}\qquad(d)\;\pi$