According to General Order 9, what should a sentry do in situations not covered by instructions?

A sentry should call the Officer of the Deck in situations not covered by instructions, as this ensures that any encounters or issues are addressed by a superior who has the authority to make decisions. The Officer of the Deck is responsible for the overall security and operational status of the assigned area and is trained to handle unexpected situations. By consulting with the Officer of the Deck, the sentry is adhering to established protocols and maintaining chain of command, which is crucial for military operations.

The other options do not align with proper protocol. Asking fellow sentries for advice may not yield the best course of action, as their judgment may not be authoritative or may vary widely. Handling it according to their own judgment can lead to incorrect or unauthorized actions that could compromise security. Leaving the post immediately would violate the duty of the sentry and could have serious consequences for the overall safety of the area being guarded. Thus, calling the Officer of the Deck is the correct and responsible action to take.