The correct answer is B) Automatic regulation of pressure or vacuum in enclosed spaces. Pressure-vacuum relief valves are designed to automatically regulate the pressure or vacuum in enclosed spaces, such as cargo tanks or other compartments, to prevent dangerous pressure or vacuum buildup. These valves open to allow air to flow in or out of the space as needed, maintaining the appropriate pressure balance and protecting the structural integrity of the enclosed area. The other answer choices do not accurately describe the primary purpose of pressure-vacuum relief valves on ships or in other maritime applications.