The correct answer is D) pressure relief device. According to 46 CFR Part 58, which covers marine engineering equipment and systems, all refrigeration systems are required to have a pressure relief device. This is to provide protection against excessive pressure buildup, which could be hazardous. The pressure relief device allows the system to safely release pressure if it exceeds a certain threshold, preventing potential damage or explosions. The other options, such as a refrigerant receiver, high pressure cut-out, or low pressure cut-out, may be important components of a refrigeration system, but they are not specifically required for protection purposes under the regulations outlined in 46 CFR Part 58.