In process costing, why are costs often divided into two main classifications? A. Process costing systems separate costs into cost categories according to the timing of when costs are introduced into the process. Often, only two cost classifications, direct materials and conversion costs, are necessary. Direct materials are frequently added at the start or end of the process and conversion costs are often added throughout the process. B. Process costing systems separate costs into cost categories according to the type of product or service being provided. Direct materials are applicable only to the manufacture of a product and conversion costs are applicable only when a service is being provided. C. Process costing systems separate costs into cost categories according to the inventory method being used. Indirect costs are used under the weighted-average method and direct costs are used under the FIFO method. D. Process costing systems separate costs into cost categories according to the timing of when costs are introduced into the process. Often, only two cost classifications, fixed and variable costs, are necessary. Fixed costs are only added at the start of the process and variable costs are added at the end.