The correct answer is A) increase reserve buoyancy. Increasing the reserve buoyancy of a vessel is the key factor in allowing it to withstand greater flooding without sinking. Reserve buoyancy refers to the amount of additional buoyant volume in the vessel's design that can displace water and keep the vessel afloat even when partially flooded. By increasing this reserve buoyancy, the vessel can tolerate a greater influx of water before reaching the point of sinking. The other options are incorrect because: B) ballasting the vessel does not directly increase the overall buoyancy, C) raising the center of gravity makes the vessel less stable, and D) lowering the center of gravity does not increase buoyancy.