Apartment

Class C properties were built within the last 30 to 40 years. They generally have blue-collar and low- to moderate-income tenants, and the rents are below market. This is where you'll find many tenants that are renters "for life." On the other hand, some of their tenants are just starting out. And as they get better jobs, they work their way up the rental scale.
Class D properties are where you'll find many Section 8 in the US or government-subsidized housing tenants. They are generally positioned in lower socioeconomic areas.