Eileen smiles wherever she goes. She smiles a lot in the classroom, which in turn prompts her fellow students to smile, making them feel happier too. This effect is best explained by which of the following theories of emotion?

This effect is best explained by the facial feedback theory.

Explanation:

The facial feedback theory states that your facial expression influences your emotion and how you feel.

In this scenario, other students in Eileen's class respond to her smile by smiling in response which automatically causes them to feel happy.