The correct answer is B) Decreasing the speed of rotation will decrease the discharge pressure. This is because the fundamental principle of a centrifugal pump is that the discharge pressure is directly proportional to the speed of rotation. As the impeller rotates faster, it imparts more kinetic energy to the fluid, resulting in a higher discharge pressure. Conversely, decreasing the speed of rotation will reduce the discharge pressure. Options A and C are incorrect because they do not accurately describe the characteristics of centrifugal cargo pumps. Centrifugal pumps are not inherently self-priming, and opening the discharge valve wider will not increase the discharge pressure - it will actually decrease the pressure due to the reduced resistance in the system.