What is an activity-based approach to refining a cost assignment system? A. An activity-based approach refines a costing system by focusing on individual activities as the fundamental cost objects. It uses the cost of these activities as the basis for assigning costs to other cost objects such as products or services. B. An activity-based approach describes a particular costing approach that uses broad averages for assigning the cost of resources uniformly to cost objects C. An activity-based approach traces direct costs to a cost object by using the actual direct-cost rates times the actual quantities of the direct-cost inputs. Indirect costs are allocated based on the actual indirect-cost rates times the actual quantities of the cost-allocation bases D. None of the above