According to the CIP standards, what must Responsible Entities control?

The choice that emphasizes physical access control based on need as determined by the Responsible Entity is correct because it aligns with the fundamental principles established in the NERC CIP standards. These standards are designed to ensure that access to critical assets and facilities is restricted to individuals who require it for their job functions, thereby reducing the risk of unauthorized access that can lead to security breaches or disruptions in operations.

By focusing on the principle of "need," Responsible Entities can implement a risk-based approach to access control that considers the specific responsibilities and functions of individuals within the organization. This method not only helps in safeguarding sensitive information and resources but also supports compliance with regulatory requirements outlined in the CIP standards.

In contrast, approaches such as making access decisions based on general consensus, employee seniority, or without documented guidelines are inconsistent with the rigorous requirements for access control. Such methods can lead to ambiguity and may expose the organization to unnecessary risks, as they do not ensure that access is granted based on well-defined, justifiable criteria. Effective access control should always be structured and well-documented to maintain the integrity of cybersecurity measures deployed in accordance with NERC CIP standards.