A useful performance standard should be clear, measurable, objective, and capable of consistent evaluation.
"All customer inquiries should be answered within seven days of receipt" is specific and testable. Internal audit can select inquiries, compare receipt dates with response dates, and determine compliance. Option A is weak because "kept to a minimum" is vague and does not define an acceptable benchmark. Option B is also vague because "promptly" is subjective unless a time requirement is defined. Option C describes desired behavior, but "positive attitude" is difficult to measure objectively without additional criteria. In evaluating performance, auditors should prefer standards that support evidence-based testing and reliable conclusions.
Therefore, Option D is the most useful standard.