Final answer:
The effectiveness of a data center's access controls can be determined through audit procedures like reviewing policies, inspecting logs, interviewing staff, and conducting walk-throughs.
Step-by-step explanation:
An auditor can best determine the effectiveness of a data center's access controls by performing various audit procedures. These procedures may include reviewing and testing the access control policies and procedures, inspecting physical access logs, interviewing employees, and performing a walk-through by attempting to access the data center without proper authorization. Additionally, the auditor could use a test of controls, where they check to see if the control activities are being applied consistently and effectively over some time.