The concept of due professional care in internal auditing involves applying the care and skill expected of a reasonably prudent and competent auditor. This includes understanding the appropriate steps and techniques for various types of engagements, including consulting engagements. Demonstrating a good understanding of the steps involved in carrying out a consulting engagement (Option C) aligns with the IIA Standard 1220: Due Professional Care, which requires internal auditors to apply the necessary care and skill in their work. This understanding is essential for executing their duties effectively and ensuring that engagements are conducted with appropriate rigor and thoroughness.
IIA Standards, Standard 1220: Due Professional Care
IIA's International Professional Practices Framework (IPPF)

The use of judgment in designing, implementing, and conducting internal control is essential and enhances management's ability to tailor controls to the organization's unique circumstances, thereby making better decisions. However, it cannot guarantee perfect outcomes as it involves estimating and forecasting future conditions, which are inherently uncertain.
COSO Internal Control Framework

Internal auditors may provide consulting services relating to operations for which they had previous responsibilities, provided they do not currently have any operational responsibilities that would impair their objectivity. This scenario is possible under IIA guidelines as long as any potential conflicts of interest are managed, and auditors maintain their independence regarding the areas they are auditing.
IIA ' s International Standards for the Professional Practice of Internal Auditing, specifically standards on objectivity and independence in consulting roles.

Due professional care required of internal auditors includes considering the cost of assurance in relation to potential benefits. This reflects the need to balance resource expenditure against the significance and risk of the audit area, ensuring that audit efforts are both efficient and effective. This principle is a fundamental aspect of professional judgment and prudent decision-making in internal auditing.
IIA Standard on Due Professional Care.