Answer:
A. the expansion of the universe
C. the helium abundance
D. the cosmic microwave background
Explanation:
Cosmology is a branch of astronomy that deals with how the universe was formed,different processes that occurred and the eventual destiny of the universe at the end.
Cosmology employed the use of bing bang theory to make findings about the universe.
The expansion of the universe, helium abundance and cosmic microwave background are the major observations in cosmology as they help in explaining some occurrences.
The observations that must be explained by any theory of cosmology are;
A: The expansion of the universe
D: The cosmic microwave background
The observations that must be explained are;
1) Universe Expansion; This was observed by Doppler when he stated that light that is travelling from galaxies that are the farthest are red shifted. Thus, it is possible on the condition that the galaxy is moving far away from the direction of the observer.
2) Cosmic Microwave background radiation; This has an acronym of CMBR and it means that during the birth of the universe, the radiation was produced and it was made to spread in every place of the universe which led to a small amount of temperature in the universe like a microwave radiation.
Read more about theory of cosmology at; https://brainly.com/question/9679125
