Concept:Fixed costs are business expenses that remain constant regardless of the level of output produced.Explanation:Rent and administrative expenses, such as office rent and management salaries, must be paid even if the business produces nothing.These costs do not increase or decrease with changes in production volume in the short run.This makes them examples of fixed costs, not variable costs.Average fixed costs refer to the fixed cost per unit of output, which is a different measure.Answer:C. fixed costs.