Final answer:
A valid real estate listing must be in writing and include the essential components of a contract, which involve an offer, acceptance, consideration, and legally competent parties. Therefore correct option is C
Step-by-step explanation:
A valid listing of real estate must be in writing and include the essential elements of a contract. According to law, for a real estate contract to be enforceable, it must be in writing and must include the fundamental components that constitute a contract. These elements include an offer, acceptance, consideration, and legally competent parties with the legal authority and capacity to enter into the contract.
Since individuals or firms must own the property to enter into a contract and this ownership bestows upon them the right to contract with others concerning the property, both of these criteria are essential for a valid listing. Therefore, the correct answer is c. both a and b.