The IIA's Standards require that an external assessment of an organization's internal audit activity must be conducted at least once every five years. Option A is the only acceptable approach listed that aligns with these standards. It involves conducting a self-assessment with independent validation by a qualified and experienced internal auditor, followed by scheduling an external assessor who is also qualified and independent. This process ensures compliance with the IIA's requirement for external assessments, maintaining both the credibility and objectivity of the internal audit activity.References: The Institute of Internal Auditors (IIA) - Standards for the Professional Practice of Internal Auditing

The most effective type of fraud test for looking for possible fictitious vendors would be running checks to uncover post office box addresses that match employee addresses. This test directly targets a common tactic used in vendor fraud schemes, where employees might set up fictitious vendor accounts and direct payments to themselves via P.O. boxes.References: IIA resources on auditing for fraud, which often discuss various methods for detecting fictitious vendors, including address comparisons.