【正确答案】 A

【答案解析】Advertising expenses are high for firms in monopolistic competition. Not only because firms need to inform consumers about the unique features of a firm"s products, but also to create or increase a perception of differences between products that are actually quite, similar. Advertising costs increase average total costs, but the increase to average total cost attributable to advertising decreases as output increases because more fixed advertising dollars are being averaged over a larger quantity. If advertising increases output (sales) significantly, it can actually decrease a firm"s average total cost if there are economies of scale.