Objectivity is one of the ethics principles for internal auditors, which means that they should not allow bias, conflict of interest, or undue influence to impair their professional judgment2. By attending a weekend social event paid for by the head of procurement, the engagement supervisor is potentially violating this principle, as it may create a personal or professional relationship that could compromise their objectivity in the procurement assurance engagement3.
References:
1: CIA Exam Practice Questions - Certified Internal Auditor 2019
2: Global Internal Auditing Code of Ethics | The IIA1, p. 1
3: Code of Ethics - The Institute of Internal Auditors or The IIA2, p. 1

The situation that presents the lowest risk of impairing an internal audit activity's independence is when senior management provides feedback on the scope of the internal audit plan. This allows for collaborative planning while still maintaining the internal audit's independence in performing its duties, as the final audit scope decisions remain with the internal audit activity.References: IIA standards on independence, which discuss the need for internal audit to maintain control over audit scopes while considering input from senior management to ensure relevant and effective audit coverage.

The situation described in option A indicates a lack of due professional care because the engagement supervisor identifies numerous deficiencies in the workpapers, such as missing evidence, incorrect references, and superfluous conclusions. Due professional care requires internal auditors to apply the diligence and skill expected of a reasonably prudent and competent auditor. The presence of these issues suggests that the auditor is struggling to maintain the quality and thoroughness required in audit documentation.
References:
* IIA Standard 1220: Due Professional Care
* IIA Practice Guide: Audit Documentation

Setting unrealistic targets for staff to achieve is a potential red flag indicating that there may be fraudulent activities occurring within the organization. When senior management sets targets that are unattainable, it can create pressure on employees to engage in unethical or fraudulent behavior to meet these goals. This is one of the elements of the fraud triangle (pressure, opportunity, and rationalization) that can lead to fraudulent activities.
References:
* IIA Practice Guide: Fraud and Internal Audit
* COSO Fraud Risk Management Guide

Demonstrating due professional care involves thorough testing and evaluation of evidence. The internal auditor exhibited due professional care by selecting a sample of purchase orders above a specific threshold and obtaining documentation for each to verify compliance with the required bidding process. This methodical approach ensures that audit findings are based on sufficient, appropriate evidence and that conclusions about the effectiveness of controls are well-supported.References: International Standards for the Professional Practice of Internal Auditing, particularly those related to due professional care and evidence evaluation.