The correct answer is A. cost driver.
A cost driver is a variable such as activity that causes cost over a given time. For example, the number of units produced is a cost driver for the cost of direct materials, and the number of machine hours is a cost driver for the cost of factory overhead.
A cost behavior is the way in which a cost changes in response to changes in the level of activity. Costs can be classified into three categories: variable costs, fixed costs, and mixed costs.
A cost center is a responsibility center in which costs are accumulated. Cost centers are used to control costs and to measure the performance of managers.
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