Following are five series of costs A through E measured at various volume levels. Identify each series as either fixed, variable, mixed, step-wise, or curvilinear. Volume (Units) 0 400 800 1,200 1,600 2,000 2,400 Series A $ 4,800 9,600 14,400 19,200 24,000 28,800 Series B $4,000 4,600 5,200 5,800 6,400 7,000 7,600 Series c $ 7,500 8,250 9,000 10,250 12,000 16,875 Series D $4,000 4,000 5,000 5,000 6,000 6,000 7,000 Series E $8,000 8,000 8,000 8,000 8,000 8,000 8,000 Series A Series B Series C Series D Series E