A linearly polarized electromagnetic wave given as $E=E_{0} \hat{i} \cos (k z-\omega t)$ is incident normally on a perfectly reflecting infinite wall at $z=\mathrm{a}$. Assuming that the material of the wall is optically inactive, the reflected wave will be given asa)$E_{r}=-E_{0} \hat{i} \cos (k z-\omega t)$b)$E_{r}=E_{0} \hat{i} \cos (k z+\omega t)$c)$E_{r}=-E_{0} \hat{i} \cos (k z+\omega t)$d)$E_{r}=E_{0} \hat{i} \sin (k z-\omega t)$