A seller and a buyer have dealt with each other in hundreds of separate grain contracts over the last five years. In performing each contract, the seller delivered the grain to the buyer and, upon delivery, the buyer signed an invoice that showed an agreed upon price for that delivery. Each invoice was silent in regard to any discount from the price for prompt payment. The custom of the grain trade is to allow a 2% discount from the invoice price for payment within 10 days of delivery. In all of their prior transactions and without objection from the seller, the buyer took 15 days to pay and deducted 5% from the invoice price. The same delivery procedure and invoice were used in the present contract as had been used previously. The present contract called for a single delivery of wheat at a price of $300,000. The seller delivered the wheat and the buyer then signed the invoice. On the third day after delivery, the buyer received the following note from the seller: “Payment in full in accordance with signed invoice is due immediately. No discounts permitted.” s/Seller. Which of the following statements concerning these facts is most accurate? A. The custom of the trade controls, and the buyer is entitled to take a 2% discount if he pays within 10 days. B. The parties’ course of dealing controls, and the buyer is entitled to take a 5% discount if he pays within 15 days. C. The seller’s retraction of his prior waiver controls, and the buyer is entitled to no discount. D. The written contract controls, and the buyer is entitled to no discount because of the parol evidence rule. Please explain your answer in the comments.