A contract is based upon an agreement. An agreement arises when one person, the offeror, makes an offer and the person to whom is made, the offeree, accepts. There must be both an offer and an acceptance. An offer can be withdrawn before acceptance and therefore prevent a contract from arising. If an offer is terminated, an attempted acceptance after the termination has no legal effect. Ordinarily, an offer may be revoked at any time by the offeror. All that is required is the showing by the offeror of his intent to revoke the offer and communication of this intent to the offeree.