Concept:An agent is a person authorised to act on behalf of another to create a contract with a third party.Explanation:The principal gives the agent authority to represent him.The agent’s role is to bring the principal and a third party into a contractual relationship.This matches the legal definition of an agent under the law of agency.An arbiter settles disputes, an auctioneer sells at auction, and middlemen may facilitate trade but do not necessarily create a binding contract for the principal.Answer:C. an agent