单选题 In perfectly competitive constant-cost industries and perfectly competitive increasing-cost industries, respectively, what is the most likely long-run effect of a permanent increase in demand? ncreasing-cost industry Constant-cost industry ①A. price decreases price decreases ②B. price decreases price remains unchanged ③C. price remains unchanged price decreases A. ① B. ②C. ③

【正确答案】 B

【答案解析】In the case of constant-cost industries, the long-run supply curve is perfectly elastic or horizontal. Therefore, a permanent increase in demand would have no effect on the price in the long run. In the case of an increasing-cost industry, the long-run supply curve slopes upward and a permanent increase in demand would result in :an increase in the price.