The API classification system for oils is divided into which two categories?

The API (American Petroleum Institute) classification system for oils is essential for understanding the properties and applications of different motor oils. The system categorizes oils into two main categories: "C" for diesel engine oils and "S" for gasoline engine oils.

The "C" category encompasses oils specifically designed for compression ignition engines, such as those found in diesel vehicles. These oils are formulated to withstand the demanding conditions of diesel operation, providing adequate lubrication, cleanliness, and engine protection against wear and deposits.

On the other hand, the "S" category is tailored for spark ignition engines, typical of gasoline-powered vehicles. Oils in this classification aim to optimize engine performance and address requirements like engine cleanliness, protection against wear, and resistance to oxidation.

Thus, knowing that the API classification system divides motor oils into these two essential categories helps users select the appropriate oil based on their engine type, ensuring optimal performance and longevity. The other options do not represent the established designations used by the API and therefore do not reflect the correct structure of the classification system.