影响边际成本曲线的外部经济，对于得出一条负斜率的行业供给曲线是非常重要的——图5.11即以这种情况说明上面相同的观点。

Figure 5.11 illustrates the same point for the case in which external economies affecting marginal cost curves are sufficiently important to yield a negatively sloping supply curve to the industry.

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而如果行业的要素供给曲线是正斜率的话，所有厂商就不可能在价格不变的情况下同时得到更多的生产要素。

But if factor supply curves to the industry slope positively, all firms together cannot get an increased quantity of factors of production at an unchanged price.

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现在，也许可以认为行业面对的这些要素的供给曲线是水平的。

Now it may be that the supply curves to the industry of these factors can be taken as horizontal.

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