The correct answer is A. Billing schemes often exploit weak segregation of duties in purchasing, receiving, and payment functions. If one person or department can request goods, approve receipt, authorize payment, and process invoices without independent verification, fictitious invoices, pass-through schemes, personal purchases, or inflated vendor billings are easier to conceal. Karen should therefore determine whether these functions operate independently. Option B is not the strongest choice as written because identifying employees with the same phone number does not directly test vendor billing fraud. Customer complaints about sales policies relate to revenue or consumer issues, not purchasing fraud. Accounts receivable and credit sales analysis is more relevant to revenue fraud. The ACFE materials classify billing schemes under fraudulent disbursements and emphasize purchasing, receiving, and invoice controls.

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