Why Does the Big Bang Theory Predict That the Cosmic

Multiple Choice

Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?

A) The background radiation came from the heat of the universe,with a peak corresponding to the temperature of the universe.
B) The spectrum of pure hydrogen is a perfect thermal radiation spectrum.
C) The spectrum of 75 percent hydrogen and 25 percent helium is a perfect thermal radiation spectrum.
D) The light from all the stars and gas in the sky averaged over the entire universe is a perfect thermal radiation spectrum.
E) It doesn't predict that the cosmic background radiation should have a perfect thermal radiation spectrum.