Some organizations group activities into four cost categories, called the hierarchy of costs, to help managers form cost pools for activity-based costing purposes. The cost hierarchyCredit for developing the cost hierarchy is generally given to R. Cooper and R. S. Kaplan, “Profit Priorities from Activity-Based Costing,” Harvard Business Review, May 1991, 130-35.groups costs based on whether the activity is at the facility level, product or customer level, batch level, or unit level. What is the difference between each of these categories, and how does this information help managers?