The correct answer is the following.
¿Quién participó en las actividades?
We are talking about the verb "to participate."
This verb can be conjugated in the following ways:
Yo participo. I participate.
Tú participas. You participate.
Él participa. He participates.
Ella participa. She participates.
Nosotros participamos. We participate.
Ellos participan. They participate.
