Which of the following would best serve to deter unethical behavior and encourage internal auditors...

Ongoing monitoring and periodic internal quality assessments best serve to deter unethical behavior and encourage objectivity among internal auditors. These quality assessments ensure that audit activities conform to professional standards and that auditors uphold principles such as objectivity. This approach provides a structured and systematic review of audit processes and practices, which reinforces the importance of adherence to ethical standards and professional conduct.

IIA guidance on ethics and objectivity, and Standard 1300: Quality Assurance and Improvement Program.