The correct answer is A) Class "A". A burning mattress is considered a Class "A" fire, as it involves ordinary combustible materials such as wood, paper, cloth, and plastics. Class "A" fires are the most common type of fire and are fueled by ordinary solid materials. The other classes of fire - Class "B" (flammable liquids and gases), Class "C" (energized electrical equipment), and Class "D" (combustible metals) - do not apply to a burning mattress situation.