Final answer:
PDGM Case Mix Subgroups refer to a system for categorizing patient care needs in the healthcare field.
Step-by-step explanation:
The PDGM Case Mix Subgroups refer to a c) system for categorizing patient care needs. These subgroups are a classification system used in the field of healthcare to identify different levels of care required by patients. They help healthcare professionals determine the appropriate services and resources needed for each patient based on their specific care needs.