Answer the following question given this paragraph: 

Ancestors of mammals evolved close to 300 million years ago. They were amniotes called synapsids. Figure below shows how modern mammals evolved from synapsids. The stages of evolution from synapsids to mammals are described below.


Q: How long ago did the ancestors of mammals evolve?

 Choices:

- 10 million

- 50,900 million years

- 100 million

- 300 million years

A:
300 million years
