Sparkling Brilliance of Diamond

The total internal reflection of light is used in polishing diamonds to create a sparking briliance. By polishing the diamond with specific cuts, it is adjusted so that most of the light rays approaching the surface are incident with an angle of incidence more than critical angle. hence they suffer multiple reflections and ultimatley come out of the diamond from the top. This gives the diamond a sparkling brilliance.
Light cannot easily escape a diamond without multiple internal reflections this is because:

Options

A. Its critical angle with reference to air is too large.
B. It critical angle with reference to air is too small.
C. The diamond is transparent.
D. Rays always enter at angle greater than cricitcal angle.