What is a requirement for a sentry when challenged at their post?

A sentry's primary responsibility is to maintain the security and integrity of their assigned post. When challenged, the sentry must adhere to established protocols that ensure only authorized personnel are allowed access to sensitive areas or information. This requires the sentry to challenge all individuals approaching their post, irrespective of any familiarity that might exist. By allowing only those with proper authorization to pass, the sentry fulfills their duty of safeguarding the area and preventing unauthorized access, which is crucial in maintaining operational security.

The other options do not adhere to the essential security measures expected of a sentry. Allowing individuals to pass based solely on familiarity undermines the very purpose of the role. Ignoring challenges late at night could lead to security breaches, and calling for backup when challenged may not be a necessary first step, as the sentry should first challenge and assess the situation based on established protocols. Thus, requiring the challenge and verification of authority is a foundational expectation for a sentry at their post.