Final answer:
The auditor should follow both The IIA Standards and any additional governmental standards when performing governmental grant compliance audits in the United States.
Step-by-step explanation:
When performing governmental grant compliance audits in the United States, the auditor should follow both The IIA Standards and any additional governmental standards. The IIA Standards provide a comprehensive framework for internal auditing that covers all aspects of the internal audit process, while the governmental standards specifically address compliance with government grants.
By following both sets of standards, the auditor ensures that they are meeting the requirements of both the public accounting profession and the government.