To ensure that recommendations for enhancing internal controls have been effectively implemented, the internal auditor should conduct appropriate testing to verify management responses. This involves re- performing procedures, reviewing documentation, and possibly observing operations to confirm that the corrective actions have been adequately executed and are effective. Simply seeking a management assurance declaration (Option B) or observing corrective measures (Option A) may not provide sufficient evidence of proper implementation. Following up during the next scheduled audit (Option C) may delay the verification process, potentially allowing risks to persist.
IIA Standard 2500: Monitoring Progress.
IIA Practice Guide on Follow-up Processes in Internal Auditing.

When assigning tasks to audit team members, the auditor in charge primarily considers factors that directly affect the quality and efficiency of the audit, such as the auditors' experience and availability, as well as the need for outside resources. While the sufficiency of budgeted hours is important for overall audit planning, it is not a direct factor in the assignment of specific tasks to team members. The assignment is more focused on ensuring that the right skills are matched to the tasks and that resources are properly coordinated with client availability. References:
* IIA Standards - 1200: Proficiency and Due Professional Care
* IIA Practice Guide - Coordination and Reliance: Developing an Assurance Map

According to the IIA's Standards, specifically Standard 1210 - Proficiency, internal auditors must possess the knowledge, skills, and other competencies needed to perform their individual responsibilities. If the internal audit activity lacks the necessary skill set to conduct a requested consulting engagement, the most appropriate action for the CAE is to decline the engagement request. This ensures that the internal audit activity does not compromise the quality and effectiveness of its services.
Reference: IIA Standard 1210 - Proficiency

According to IIA guidance, curiosity is a key attribute that indicates a candidate's ability to probe further when reviewing incidents that have the appearance of misbehavior. Curiosity drives the auditor to ask deeper questions, seek out underlying causes, and thoroughly investigate anomalies. While integrity (Option A), flexibility (Option B), and initiative (Option C) are important qualities for an internal auditor, curiosity specifically relates to the propensity to investigate and uncover the truth behind incidents.
IIA Standard 1200: Proficiency and Due Professional Care.
IIA Practice Guide on Competency Framework for Internal Auditing.

The most effective step in helping the auditor determine whether fraud exists after observing a double payment transaction on a supplier invoice is to perform data analytics on the supplier's information, invoiced amounts, and payments performed. Data analytics allows the auditor to systematically analyze large volumes of transactions to identify patterns, anomalies, and potential fraudulent activities. This approach is more comprehensive and effective in uncovering fraud than simply extending the audit scope or switching to a fraud investigation engagement without a thorough initial analysis.
IIA Standards: 1220.A1 - Due Professional Care
IIA Practice Guide: Auditing for Fraud