The correct answer is C) Centrifugal pump. Centrifugal pumps must always be primed, meaning they need to be filled with the liquid they will be pumping before they can function properly. This is because centrifugal pumps rely on the liquid's momentum to create the necessary suction and pressure, and they cannot generate this momentum on their own when the pump is dry. In contrast, reciprocating pumps and rotary pumps can often start and operate without being primed, as they use positive displacement to move the liquid rather than relying on the liquid's momentum. Therefore, options A and B are incorrect.