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 $ 3,600 4,200 4,800 5,400 6,000 6,600 7,200 Series B $ 0 7,100 7,810 8,520 9,703 11,360 15,975 Series C $ 3,200 3,200 4,200 4,200 5,200 5,200 6,200 Series D $ 7,200 7,200 7,200 7,200 7,200 7,200 7,200 Series A Series B Series C Series D Series E