The correct answer is A) The pump delivers full capacity when started, but gradually slackens off to an abnormally low flow. Excessive air leakage into the suction side of a centrifugal pump would cause the pump to initially deliver full capacity, but the air leakage would gradually reduce the pump's ability to draw in fluid, resulting in a gradual decrease in flow. This is because the air entering the suction side disrupts the pump's ability to create the necessary vacuum to draw in fluid, causing the pump's performance to degrade over time. The other answer choices do not directly relate to the symptoms of excessive air leakage. Overloading the motor (B), overheating the packing gland (C), and pounding noises (D) can be caused by various other issues, but are not the primary symptoms of air leakage on the suction side of a centrifugal pump.