Responding to County's written advertisement for bids, Tyres was the successful bidder for the sale of tires to County for County's vehicles. Tyres and County entered into a signed, written agreement that specified, "It is agreed that Tyres will deliver all tires required by this agreement to County, in accordance with the attached bid form and specifications, for a one-year period beginning September 1, 1990." Attached to the agreement was a copy of the bid form and specifications. In the written advertisement to which Tyres had responded, but not in the bid form, County had stated, "Multiple awards may be issued if they are in the best interests of County." No definite quantity of tires to be bought by County from Tyres was specified in any of these documents. In January 1991, Tyres learned that County was buying some of its tires from one of Tyres's competitors. Contending that the Tyres-County agreement was a requirements contract, Tyres sued County for the damages caused by County's buying some of its tires from the competitor. If County defends by offering proof of the advertisement concerning the possibility of multiple awards, should the court admit the evidence? 
Yes, because the provision in the written agreement, "all tires required by this agreement," is ambiguous.  Yes, because the advertisement was in writing.  No, because of the parol evidence rule.  No, because it would make the contract illusory. 