A control question has been asked. In comparing our actual costs against the budget set for this department, can we separate the specific costs of our activities from our share of the general overheads?" Which is the most useful classification of costs for answering this control question? Select one: a. Fixed and variable costs of the department b. Product and period costs of products of the department c. Direct and indirect costs related to the department d. Relevant and non-relevant costs for the department