On small passenger vessels, shut-off valves must be installed on both gasoline and diesel fuel supply lines __________.

Correct Answer: Option A — at the tank and the engine end of the fuel line

To ensure positive fuel isolation, 46 CFR requires shut-off valves at both the tank and the engine end of gasoline and diesel fuel lines. This configuration allows the crew to isolate the fuel supply at the source and at the engine, preventing fuel flow during maintenance or emergencies.