What should the sentry do as per General Order 9?

The correct answer is that the sentry must call the petty officer in any case not covered by instructions. General Order 9 emphasizes the importance of knowing when to seek guidance and clarification. It is critical for a sentry to be aware of their limits and the specific instructions they have been given. When faced with a situation that isn't explicitly addressed in their training or standing orders, contacting a petty officer ensures that the sentry can receive authoritative guidance on how to proceed. This helps maintain security and order, as the petty officer likely has more experience and a broader understanding of the protocols in place.

Other options suggest actions that may not align with the priority of seeking proper instruction. For instance, relaying all orders received does not address the need for guidance in unforeseen circumstances, and reporting to fellow sentries may not provide the necessary authority or clarity that a petty officer can offer. It is essential for a sentry to act responsibly—seeking out the appropriate chain of command when the situation demands it.