Final answer:
The internal auditor's conclusions are most affected by their inquiry and interviews, as they provide valuable information for making informed conclusions.
Step-by-step explanation:
The internal auditor's conclusions are most affected by their inquiry, which involves a critical examination of the sources of information. By asking questions about the reliability and perspective of the sources, the internal auditor can make informed conclusions. Additionally, interviews can also play a role in the internal auditor's conclusions, as they provide valuable insider information about the subject of the audit.