Final answer:
The auditor's findings suggest a need for additional testing to assess the effectiveness of accounting controls and to address the risk of duplicate payments, which is highlighted by Noel's discovery of a significant overpayment error. The correct option is: 1).
Step-by-step explanation:
When an auditor finds several accounts payable vouchers requiring adjustments for duplicate payment of prior invoices, this suggests a need for additional testing to determine the effectiveness of related controls and the current risk of making duplicate payments to suppliers. In this context, Noel's discovery of a $250,000 overpayment error highlights the need for vigilant checks within the accounting process. The fact that no one else noticed the error apart from Noel indicates that there may be insufficient controls in the system. Rather than pointing to a sophisticated system, these issues signal a likely need for improvement in the controls to prevent overpayments.