Answer:
1. Microwave Background - Very early in its history, the whole Universe was very hot. As it expanded, this heat left behind a "glow" that fills the entire Universe. The Big Bang theory not only predicts that this glow should exist, but that it should be visible as microwaves - part of the Electromagnetic Spectrum. This is the Cosmic Microwave Background which has been accurately measured by orbiting detectors, and is very good evidence that the Big Bang theory is correct.
2. Redshift of Galaxies - The redshift of distant galaxies means that the Universe is probably expanding. If we then go back far enough in time, everything must have been squashed together into a tiny dot. The rapid eruption from this tiny dot was the Big Bang.
3. Mixture of Elements - As the Universe expanded and cooled down, some of the elements that we see today were created. The Big Bang theory predicts how much of each element should have been made in the early universe, and what we see in very distant galaxies and old stars is just right.
Explanation:
