The audit team that will be most effective in performing an internal department audit is...

Independence and objectivity are fundamental to effective internal audits. Including individuals from the audited department creates a conflict of interest and compromises the audit's impartiality.

While familiarity with the department's processes is beneficial, auditors should come from outside the department to provide a fresh, unbiased perspective.

Including managers (C) or higher-level executives (D) can introduce intimidation and pressure on the auditors, undermining the audit's integrity.

References:

ASQ CMQ/OE Handbook, Section VI: Quality Systems (discussions on internal audits, auditor independence, and objectivity)