According to IIA guidance, due professional care means that internal auditors must apply the care and skill expected of a reasonably prudent and competent internal auditor. This involves considering the cost of assurance in relation to potential benefits and exercising judgment and care in accordance with the complexity of the task. It does not imply an exhaustive review of all transactions or guarantees that all significant risks will be identified or that fraud does not exist.
The Institute of Internal Auditors (IIA) - International Standards for the Professional Practice of Internal Auditing, specifically those related to due professional care.

The inclusion of the clause stating that engagements are conducted in conformance with the International Standards for the Professional Practice of Internal Auditing can be justified if internal audit activity policies and engagement records provide relevant, sufficient, and competent evidence that the statement is correct.
This evidence shows adherence to the Standards in audit planning, execution, and reporting, ensuring the quality and reliability of audit results as per the Standards' requirements.
International Standards for the Professional Practice of Internal Auditing; guidelines on quality assurance and improvement programs.

Workshops are likely the most efficient way for management to self-assess the overall effectiveness of the controls in a 200-person manufacturing department. Workshops can facilitate interactive discussions and group activities that help identify control gaps, understand employee perspectives, and consolidate feedback effectively across a large group.
Best practices in internal control assessments and organizational development literature.

Skimming is the type of fraud that involves an employee accepting cash payments and failing to record the sales, thereby diverting the cash for personal use. This kind of fraud occurs before the transaction is recorded in the accounting records, making it particularly stealthy since it does not directly affect the accounting system.
Fraud classification and types in internal audit literature

A conflict of interest is a situation where an internal auditor's personal or professional interests may compromise their objectivity, integrity, or ability to perform their work effectively. A conflict of interest policy is a document that defines what constitutes a conflict of interest, how to identify and report it, and how to manage or resolve it. Therefore, option D is the best answer.