The Doppler Effect talks about the frequency of sound and light as the source and person move. So, <em>When light waves are emitted by a moving source, scientists can measure</em> = the Doppler effect.
Cosmic microwave background radiation has the word "cosmic" in it, so you can assume it has to do with space automatically. There is radiation in space too, so I'm pretty sure that <em>The extremely low temperature of outer space can be explained as </em>= cosmic microwave background radiation.
Particle accelerators are these big machines that usually smash protons/electrons together, so <em>Scientists smash together tiny bits of matter using </em>= particle accelerators.
And now, by process of elimination and because the Big Bang Theory talks about the creation of Earth, we know that <em>Scientists extrapolate backwards in time to derive</em> = the Big Bang Theory.
