If a single cylinder relief valve on a main propulsion diesel engine begins to lift, but it is not possible to secure the engine, which of the following actions should be taken?

Correct Answer: Option B — Secure or reduce fuel to that cylinder.

A lifting relief valve indicates dangerous overpressure from excessive fuel or a stuck injector in that specific cylinder. Reducing or securing fuel immediately relieves thermal and mechanical stress, preventing catastrophic structural failure until repairs can be safely completed.