When an internal audit team leader encounters difficulties due to the lack of a system of internal controls, the most appropriate course of action is to add a consulting component to the scheduled assurance engagement.
This approach allows the internal audit team to provide advice and recommendations on establishing internal controls while still fulfilling their assurance responsibilities. By integrating consulting activities, the auditors can help the business unit improve its control environment, which can then be assessed in the assurance engagement.
The Institute of Internal Auditors (IIA) Practice Guide: Consulting Engagements IIA Standard 1130 - Impairment to Independence or Objectivity

Root cause-based recommendations are most likely to propose long-term solutions. These recommendations address the underlying causes of issues rather than just the symptoms. By identifying and addressing the root causes, the solutions implemented are more likely to be effective in preventing the recurrence of the same or similar issues in the future.
* Root Cause Analysis: This involves a thorough investigation to identify the fundamental reasons for the occurrence of a problem. It goes beyond immediate symptoms to understand the deeper issues.
* Long-term Solutions: Recommendations based on root cause analysis focus on eliminating the underlying causes, leading to sustainable improvements and reducing the likelihood of repeat issues.
* Systemic Improvements: Addressing root causes often leads to changes in processes, controls, or organizational practices, resulting in broader and more lasting benefits.
By focusing on the root cause, the recommendations provide more robust and enduring solutions, contributing to the overall improvement and resilience of the organization.
The Institute of Internal Auditors (IIA) Standards
IIA Practice Guide: Root Cause Analysis in Internal Auditing

According to IIA guidance on due professional care, internal auditors should perform thorough and adequate steps to verify the accuracy and legitimacy of transactions. When reviewing cash disbursements, it is essential to check the three-way match among the invoice, purchase order, and receiving report. This ensures that the payment is valid, authorized, and that the goods or services were actually received as ordered. This step is crucial in preventing and detecting errors and fraud, thereby ensuring that the audit findings are reliable and accurate.
IIA Standard 1220: Due Professional Care
IIA Practice Guide: Auditing Accounts Payable and Disbursements

Best practices in internal auditing emphasize the importance of follow-up on engagement outcomes to ensure that agreed-upon actions are implemented and effective. According to Standard 2500 - Monitoring Progress, the chief audit executive must establish and maintain a system to monitor the disposition of results communicated to management. This ensures that corrective actions are taken and that the internal audit function fulfills its role in improving the organization's governance, risk management, and control processes.
Allocating resources for follow-up is crucial to maintain accountability and support continuous improvement.
Institute of Internal Auditors (IIA), International Standards for the Professional Practice of Internal Auditing (Standards), Standard 2500 - Monitoring Progress.

Nonstatistical sampling allows auditors to use their professional judgment to determine the sample size and select the items to be tested. Unlike statistical sampling, which relies on probabilistic methods to determine the sample size and selection, nonstatistical sampling is more flexible and can be tailored to the specific circumstances of the audit engagement.
IIA References:
* IIA Standard 2320: Analysis and Evaluation suggests that internal auditors should apply appropriate methods to analyze data and draw conclusions. Nonstatistical sampling allows for the application of professional judgment, which can be advantageous in certain audit situations where rigid statistical methods may not be practical or necessary.
* The Practice Guide on Sampling discusses the differences between statistical and nonstatistical sampling, highlighting that nonstatistical sampling relies more on the auditor's judgment, which can be beneficial in certain contexts.
Given this, the correct answer is C. Nonstatistical sampling provides for the use of subjective judgment in determining the sample size.