Which Pronoun can be either singular or plural?

A = I

B = It

C = You

D = Them

C. You

Explanation:

A person could say to an audience "You can do this" and he is referring to everyone in the room.

Two friends could be talking to one another and say "You are my best friend" and just be referring to the one person in the room.

So you can either represent one or many people.

C. "You"

Explanation:

"You" can be either singular or plural. "You" can be used to talk about one person or more than one person and that makes it to be either singular or plural.