What action should a sentry take according to the 8th General Order?

The 8th General Order specifically instructs a sentry to "give the alarm in case of fire or disorder." This highlights the sentry's responsibility to ensure the safety and security of the area they are guarding. The duty involves being vigilant and prepared to respond to emergencies, particularly situations that could jeopardize the safety of personnel, equipment, or the mission.

This command reflects the importance of situational awareness and readiness in a military context, ensuring that potential threats or hazards are reported and managed appropriately. It emphasizes the crucial role of communication in maintaining order and responding effectively to crises.

While the other choices involve important aspects of a sentry's duties, they are focused on different responsibilities such as challenging individuals, saluting, or reporting suspicious activities, which fall under other General Orders. These duties contribute to overall security, but they do not specifically address the urgent and critical action outlined in the 8th General Order.