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) 400 see 1,200 1,600 2,000 2,400 Series A $ @ 3,600 7,200 10,800 14,400 18,000 21,600 Series B $2,500 3,100 3,700 4,300 4,900 5,500 6,100 Series C $ @ 6,000 6,600 7,200 8,200 9,600 13,500 Series D $1,000 1,000 2,000 2,800 3,000 3,000 4,000 Series E $5,000 5,000 5,000 5,000 5,000 5,000 5,000 Series A Series B Series C Series D Series E