Why Do We Expect the Cosmic Background Radiation to Be

Multiple Choice

Why do we expect the cosmic background radiation to be almost, but not quite, the same in all directions?

A) The overall structure of the universe is very uniform, but the universe must have contained some regions of higher density in order for galaxies to form.
B) The temperature of the universe can be found by taking an average over the entire sky, but individual stars will create peaks in the temperature over small angles.
C) Dark matter will smooth out the spectrum, but the small patches of "light" matter create fluctuations in the temperature.
D) The overall structure of the universe is very uniform, but the synthesis of different elements produces varying signatures within the background radiation.
E) The overall structure of the universe is very uniform, but intervening gas between us and the era of nuclei absorbs wavelengths depending on the composition and redshift of the gas.