In the era, you would see ferns, trees, and dinosaurs.

proterozoic
paleozoic
mesozoic
cenozoic

The correct answer is Mesozoic

The era when ferns, trees and dinosaurs were present is called as the Mesozoic era. The dinosaurs, trees and ferns basically appeared in the Triassic period of the Mesozoic era. They were present approximately 200 millions year ago. The dinosaurs flourished on earth and along with them there are evidences that ferns and trees also appeared at that time.

c. newton's third law of motion