A ray of light passes through four transparent media with refractive indices $\mu_1, \mu_2, \mu_3$ and $\mu_4$ as shown. The surface of all media are parallel. The emerging say CD is parallel to incident ray AB, Then ,

Question

$\begin{array}{1 1} (a)\;\mu_1=\mu_2 \\ (b)\;\mu_2=\mu_3 \\ (c)\;2 \mu_1 =\mu_3 \\ (d)\;\mu_4=\mu_1 \end{array}$