The correct answer is D) regulations about darkening ship. When a merchant vessel is under the Naval Control of Shipping Organization in wartime, naval authorities may give orders pertaining to regulations about darkening the ship. This is because the naval authorities need to enforce blackout conditions and other lighting restrictions to maintain the vessel's stealth and reduce the risk of detection by enemy forces. The other answer choices, such as minimum manning standards, stowage of explosives, and types of cargoes permitted, are not directly related to the naval control and blackout regulations during wartime.