Chris promises Doreen $40,000 if she graduates from Eagle College. Doreen enrolls in Eagle, attends full-time for four years, and graduates. When Doreen asks Chris for $40,000, Chris says: "I don't remember promising you $40,000. But if there was a promise, it's not enforceable because we didn't bargain for it. And, even if there was a promise that would otherwise be unenforceable. I revoke it now." Can Doreen enforce Chris' "promise"? Why or why not