NO.PZ2018062017000011
问题如下：
A long-run average cost curve (LRAC) has a positivie slope at present, in other words,
选项：
A. the firm is at optimal size.
B. production units increase with an increasing cost per unit.
C. the firm is experiencing economies of scale.
解释：
B is correct.
The upward sloping segment of long-run average total cost curve indicates that diseconomies of scales are at present. When number of production units increases, cost per unit increases.
考点：Economies of Scale and Diseconomies of Scale
解析：长期平均总成本曲线上升部分意味着随着产量的增加，单位成本在不断上升，所以B选项正确。
此时厂商的生产规模并非最优，企业可以减少产量，实现生产规模最优，所以A选项错误。
此时，厂商出于规模不经济阶段，而非规模经济阶段，所以C选项的说法也错误。
怎么判断slope是positive还是negative
