Which of the following is true concerning Class A fires?

Class A fires are characterized by the ignition of ordinary combustibles such as wood, paper, cloth, trash, and some plastics. When such materials burn, they produce ash as a byproduct of combustion. This is a distinctive feature of Class A fires, setting them apart from other classes that involve different materials and combustion processes.

The other options represent various categories of fires or materials involved in combustion. For instance, Class B fires relate to flammable liquids, such as gasoline and oil, while Class C fires are associated with electrical equipment. Additionally, Class D fires pertain to combustible metals like magnesium, titanium, and lithium. Each type is defined by the materials that fuel the fire, contributing to the specific methods required for extinguishing them effectively. Thus, 'C' stands out as the accurate description of Class A fires.