After extensive negotiations, Tune Corporation, a radio manufacturer, and Bill's Comex, Inc., a retailer, entered into a final written agreement in which Tune agreed to sell and Bill's agreed to buy all of its requirements of radios, estimated at 20 units per month, during the period January 1, 1988, through December 31, 1990, at a price of $50 per unit. A dispute arose in late December 1990, when Bill's returned 25 undefective radios to Tune for full credit after Tune had refused to extend the contract for a second three-year period. In an action by Tune against Bill's for damages due to return of the 25 radios, Tune introduces the written agreement, which expressly permitted the buyer to return defective radios for credit but was silent as to return of undefective radios for credit. Bill's seeks to introduce evidence that during the three years of the agreement it had returned, for various reasons, 125 undefective radios, for which Tune had granted full credit. Tune objects to the admissibility of this evidence. "For this question only, assume the following facts. When Bill's returned the 25 radios in question, it included with the shipment a check payable to Tune for the balance admittedly due on all other merchandise sold and delivered to Bill's. The check was conspicuously marked, "Payment in full for all goods sold to Bill's to date." Tune's credit manager, reading this check notation and knowing that Bill's had also returned the 25 radios for full credit, deposited the check without protest in Tune's local bank account. The canceled check was returned to Bill's a week later. Which of the following defenses would best serve Bill's?
Tune's deposit of the check and its return to Bill's after payment estopped Tune thereafter to assert that Bill's owed any additional amount. By depositing the check without protest and with knowledge of its wording, Tune discharged any remaining duty to pay on the part of Bill's.  By depositing the check without protest and with knowledge of its wording, Tune entered into a novation discharging any remaining duty to pay on the part of Bill's.  The parties' good-faith dispute over return of the radios suspended the duty of Bill's, if any, to pay any balance due.