The patrolman, while on duty on a passenger vessel, must have in his possession a(n) __________.

Correct Answer: Option D — flashlight

46 CFR 185.510 requires that a patrolman on a passenger vessel must carry a flashlight while on duty. This is a critical safety requirement to ensure the patrolman can effectively inspect spaces, identify hazards, or navigate through smoke-filled compartments during an emergency or fire watch.