Which type of assessment may include reviewing documents, system walk-thrus, traffic analysis, or ARP tables?

The correct choice focuses on Passive Assessment, which emphasizes gathering information without directly interacting with the system in ways that could alter its operation or performance. This method encompasses reviewing documents and system configurations, conducting traffic analysis, and analyzing ARP tables, all geared towards understanding the existing security posture without introducing interference.

Passive Assessments are crucial because they can identify vulnerabilities and gather significant data regarding system behavior and network activity while maintaining the system's integrity and stability. This type of assessment works by observing and collecting information quietly, which makes it particularly effective in environments where system availability is critical or when the goal is to limit potential disruption.

Other types of assessment like Active Assessment and Penetration Testing involve more direct engagement with the system, which may introduce changes or risks during the process. A Gap Assessment is more focused on comparing current practices with desired standards or benchmarks, typically highlighting deficiencies rather than analyzing ongoing activities. Hence, the nature of Passive Assessment aligns perfectly with the activities described in the question, reinforcing its role in evaluating cybersecurity in Industrial Automation and Control Systems.