In a signed writing, Barb offered to sell her business to Tom for $50,000. In this same writing, Barb promised not to revoke the offer for 30 days in exchange for $500 paid by Tom. Under these facts: The parties have entered into a legally unenforceable future agreement. The parties have entered into a legally enforceable quasi contract. The parties have entered into a legally enforceable option contract. The parties have entered into a legally enforceable right of first refusal.