Question：In activity based costing (ABC) what is a cost driver?
　　A. A mechanism for accumulating the costs of an activity.
　　B. A cost relating to more than one product or service.
　　C. An overhead cost that is incurred as a direct consequence of an activity.
　　D. A factor which causes the costs of an activity to increase or decrease.
　　The correct description of a cost driver is a factor which causes the costs of an activity to increase or decrease.
　　解析：For example, a cost driver for materials handling costs could be the number of production runs: the higher the number of production runs, the higher will be the cost of material handling.
　　A mechanism for accumulating the costs of an activity is a description of a cost pool.
　　An overhead cost that is incurred as a direct consequence of an activity is a description of an attributable overhead cost.
　　A cost relating to more than one product or service is a description of a common cost.