What action must a sentry take according to the 4th General Order?

The fourth General Order states that a sentry must "quit my post only when properly relieved." This is a crucial directive as it ensures that a sentry remains vigilant and maintains the integrity of their watch until a qualified individual has taken over the responsibility. Proper relief is essential to uphold the security and safety of the area being guarded, allowing for continuity in monitoring and deterring any potential threats. This order emphasizes the importance of accountability and the need for clear communication among personnel during transitions, preventing lapses in vigilance that could be exploited by unauthorized individuals.

Other options may address important aspects of sentry duties, such as salute protocols or communication guidelines, but they do not capture the critical nature of remaining at one's post until officially relieved, which is fundamental to effective military operations and security protocols.