Concept:In the short run, at least one factor of production is fixed, so some costs remain constant regardless of output.Explanation:The short run is a production period in which a firm cannot change all its inputs. Fixed costs are those expenditures that do not vary with output, such as rent or insurance, and they must be paid even when output is 0. Variable cost, marginal cost, and total cost all change as the level of production changes in the short run. Since only fixed costs remain unchanged during this time, it is the correct answer.Answer:D. Fixed cost