The correct answer is B) They are normally lubricated and cooled by the fluid being pumped. Mechanical seals are designed to provide a reliable seal between the rotating shaft and the stationary housing of a pump or other rotating equipment. The fluid being pumped typically provides the necessary lubrication and cooling for the dynamic seal surfaces, allowing the mechanical seal to function effectively. This is a key design feature of mechanical seals, as it eliminates the need for external lubrication systems. The other answer choices are incorrect: A) Mechanical seals can be used in salt water applications, not just in lieu of packing glands for other services. C) Mechanical seals are suitable for use on fuel oil transfer pumps, as they can handle a wide range of fluid types. D) Mechanical seals do not require periodic adjustment of the spring compression once installed. They are designed to maintain a consistent seal without the need for user intervention.