The refractive index of A and B light is greater than that of A light, and the refractive index of B light is greater than that of A light, so the frequency of A light is less than that of B light, so A is correct.

B, because the refractive index of A light is small, according to v=cn, A light propagates at high speed in the medium, so B is wrong.

C, because when light is incident from one interface and refracted to another interface, according to the geometric relationship, the angle of refraction on the first interface is equal to the angle of incidence on the second interface, so neither light can be totally reflected. So, C is wrong.

D, according to the geometric relationship, the outgoing light is not necessarily parallel to the incoming light, so d is wrong.

So choose a.