In Arizona, a contract is binding when:

Option A is incorrect because a contract cannot be binding when only one party signs. The buyer's signature alone does not constitute acceptance by the seller, leaving the contract incomplete without mutual assent.

Option B is incorrect because a seller's signature alone does not create a binding contract. The buyer must formally accept the terms and communicate this acceptance to complete the mutual assent required for a valid contract.

Option D is incorrect because earnest money deposit, while important in real estate transactions, is evidence of the contract rather than its creation. A binding contract exists when all parties have signed and acceptance is communicated, regardless of whether earnest money has been deposited.