Cell Company has discovered that the cost of processing customer invoices is strictly variable within the relevant range. Which one of the following statements concerning the cost of processing customer invoices is incorrect? a. The total cost of processing customer invoices will increase as the volume of customer invoices increases. b. The cost per unit for processing customer invoices will decline as the volume of customer invoices increases. c. The cost of processing the 100 th customer invoice will be the same as the cost of processing the first customer invoice. d. The average cost per unit for processing a customer invoice will equal the incremental cost of processing one more customer invoice. 186. When identifying fixed and variable costs, which one of the following is a typical assumption concerning cost behavior? a. General and administrative costs are assumed to be variable costs. b. Cost behavior is assumed to be realistic for all levels of activity from zero to maximum capacity. c. Total costs are assumed to be linear when plotted on a graph. d. The relevant time period is assumed to be five years