A diverging beam of light from a point source S having divergence angle a, falls symmetrically on a glass slab as shown. The angles of incidence of the two extreme rays are equal. If the thickness of the glass slab is t and the refractive index n, then the divergence angle of the emergent beam is [IIT-JEE (Screening) 2000]

• A.            Zero
• B.            a
• C.            \[{{\sin }^{-1}}(1/n)\]
• D.            \[2{{\sin }^{-1}}(1/n)\]