You are the Master of a 500-gross ton passenger vessel operating on rivers. Your vessel accidentally runs aground. Under the regulations for passenger vessels, you must notify the __________.

Correct Answer: Option A — nearest Coast Guard Marine Safety or Marine Inspection Office as soon as possible

46 CFR Part 4 requires the Master to report any marine casualty involving grounding, collision, or significant damage to the nearest Coast Guard Marine Safety Office. Immediate notification is mandatory to ensure the Coast Guard can assess potential environmental threats, navigational hazards, or the need for a formal investigation.