Which of the Following Gives the Two Main Assumptions of Theoretical

Which of the following gives the two main assumptions of theoretical models of galaxy evolution?

A) The beginning of the universe is modeled after a supernova explosion, and all elements were produced by this exploding star.
B) Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
C) Hydrogen and helium filled all of space, and the entire universe had exactly the same density everywhere.
D) The universe has always been expanding, and denser areas contracted to form the first stars.
E) The universe was composed originally only of hydrogen, and all the other elements came from stars.