Which of the following is a requirement for a valid real estate contract?

A requirement for a valid real estate contract is that it must be a written document signed by both parties. This is essential because, under California law and the Statute of Frauds, certain contracts, including those related to the sale of real property, must be in writing to be enforceable. This protects both parties by ensuring that the terms of the agreement are clear and documented, providing a legal framework for any disputes that may arise.

Verbal agreements, while they can exist, are generally not enforceable in the context of real estate transactions due to the requirement for written contracts. Additionally, the presence of witnesses is not a legal requirement for the validity of a real estate contract, although having witnesses can provide extra protection. Lastly, a mutual agreement that lacks consideration, which refers to a benefit or value exchanged between the parties, does not meet the requirements for a valid contract as there must be something of value involved to make the agreement enforceable. Thus, the correct answer emphasizes the importance of having a written and signed document for clarity and legal protection in real estate transactions.