"Perfect Mirrors" Are Made by

"Perfect mirrors" are made by

A) coating a glass surface with an extremely pure layer of silver or aluminum.
B) coating a glass surface with an extremely pure layer of silver or aluminum and then coating the metal surface with a quarter-wavelength thickness of the dielectric magnesium fluoride.
C) stacking thin layers of different dielectric materials on a glass surface.
D) heating an ordinary mirror almost to its melting point.