According to IIA guidance, demonstrating due professional care includes adequately planning and supervising the engagement, and documenting the scope and methodology of the audit procedures performed. Option B best demonstrates that internal auditors exercised due professional care by documenting the scope and methodology of the data testing, which is essential for ensuring the engagement's objectives are achieved, and any conclusions drawn are well-supported.
The Institute of Internal Auditors (IIA) - International Standards for the Professional Practice of Internal Auditing.

When an organization has a high level of risk maturity, the internal audit activity is less likely to provide consulting services related to risk management. In highly mature risk environments, organizations typically have well-established risk management processes and capabilities, thereby reducing the need for consulting services from internal audit in this area. Instead, internal audit may focus more on assurance services over the existing risk management processes to ensure they are functioning as intended.
Risk management and internal audit literature discussing the relationship between organizational risk maturity and the role of internal audit.

An internal audit charter is a formal document that defines the internal audit activity's purpose, authority, and responsibility. According to IIA standards, the charter should also establish the internal audit activity's position within the organization, including the nature of the chief audit executive's functional reporting relationship with the board. This helps ensure that the internal audit activity has sufficient authority and resources, and that there is appropriate oversight by the board.
The Institute of Internal Auditors (IIA) - International Professional Practices Framework (IPPF) - Standards regarding audit charter

While internal auditors are not primarily fraud investigators, their role does include a responsibility to demonstrate adequate professional skepticism. This means being alert to conditions that may indicate possible fraud or error while performing audit engagements. Demonstrating skepticism is essential in enabling auditors to conduct thorough and effective audits, especially concerning fraud risks.
Institute of Internal Auditors (IIA) - Practice Advisories on Fraud and Professional Skepticism.

One of the possible reasons for the failure to identify transactions between the parent organization and a subsidiary is that the auditor did not have sufficient knowledge of the group structure, the consolidation process, and the related party disclosure requirements2. The auditor should obtain an understanding of the entity and its environment, including its internal control, as part of the risk assessment procedures3. This would help the auditor to identify and assess the risks of material misstatement due to related party transactions, and design and perform appropriate audit procedures to address those risks4.
References:
1: IAS 24 - Related Party Disclosures5, p. 1 2: Group audit issues | P7 Advanced Audit and Assurance | ACCA ...2, p. 1 3: INTERNATIONAL STANDARD ON AUDITING 315 (REVISED) IDENTIFYING AND ... - IFAC1, p. 1 4: ISA 550 Related Parties - IAASB, p. 1