The following chart shows four different costs: Cost A, Cost B, Cost C, and Cost D. For each cost, the chart shows the total cost and cost per unit at two different volumes within the same relevant range. Based on this information, which of the following statement is true? At 4,000 Units At 5,000 Units Cost A Cost B Cost Cost Total Total Per Per Cost Cost Unit Unit $42,000 $10.50 $50,000 $10.00 $60,000 $15.00 $60,000 $12.00 Cost $32,000 $8.00 $40,000 $8.00 C Cost D $24,000 $6.00 $30,000 $6.00 Cost D is a variable cost. Cost A is a variable cost. Cost C is a fixed cost. Cost B is a mixed cost