Answer:
D- 13.7 billion years ago
Explanation:
According to the big bang theory, the universe started its life approximately 13.7 bilion years ago. Initially, all the matter and the energy of the universe was concentrated in a single point of infinite density, called singularity. Then, a huge and fast expansion occurs, and the universe expanded at a very fast speed: matter and energy started to separate, and they started to form the subatomic particles that we know, then atoms, molecules, and then bigger objects, such as stars and galaxies.
