The correct answer is D. Cold-spark voltage readings test lamp need not be checked before hydraulic starting of an engine on a covered lifeboat. The reasoning is that a cold-spark voltage readings test lamp is used to check the ignition system, which is not directly relevant to the hydraulic starting process. The key things to check before hydraulic starting are the pressure in the accumulator gauge, the fuel supply line valve, and the engine stop control to ensure the engine can be properly started and stopped using the hydraulic system. The other options (A, B, and C) are all important checks that should be performed to ensure the proper functioning of the hydraulic starting system and the engine's fuel supply and controls.