Final answer:
Mary Jo must join the National Association of Realtors (NAR) to become a Realtor, which is a designation for real estate professionals who abide by the NAR's code of ethics and are members in good standing.
Step-by-step explanation:
Mary Jo is a real estate licensee who'd like to become a Realtor. To achieve this, she must join the National Association of Realtors (NAR). Becoming a member of the NAR distinguishes her as a Realtor, which is a trademarked term that refers to a real estate professional who is an active member of the National Association of Realtors and adheres to its strict code of ethics. It's important to note that, to maintain this designation, she will have to abide by the NAR's standards and continue to be a member in good standing.
In contrast, passing the state licensing exam, completing additional real estate courses, or obtaining a broker's license are steps associated with becoming a real estate agent or advancing in the real estate profession but are not requirements for becoming a Realtor per se.