Which service ratings refer specifically to motor oils?

The correct answer pertains specifically to the service ratings for motor oils. The ratings identified, such as MS, SE, and SG, are recognized classifications from the American Petroleum Institute (API) and encompass a range of performance standards for motor oils, allowing consumers and mechanics to select an oil that meets certain engine requirements.

Each of these designations indicates a different level of performance, particularly in terms of engine protection and environmental considerations. For example, higher ratings generally represent improved performance and compatibility with new engine technologies compared to lower ratings.

In contrast, the other choices mix different systems of classification that may not exclusively pertain to motor oils. SAE refers to the Society of Automotive Engineers and typically addresses viscosity rather than service ratings. API and ISO are standards that encompass broader scopes but do not specifically designate the service rating categories that are unique to motor oils. The K, L, M ratings are less defined in the context of motor oil performance and do not represent established industry classifications. Thus, the set of ratings in the correct answer precisely reflects the criteria for motor oil service ratings.