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雷达卡
The rise in the price of petroleum increases production costs for individual firms and thus shifts the industry supply curve up, as shown in Figure 8.
The typical firm's initial marginal-cost curve is MC1 and its average-total-cost curve is ATC1.
In the initial equilibrium, the industry supply curve, S1, intersects the demand curve at price P1, which is equal to the minimum average total cost of the typical firm.
Thus the typical firm earns no economic profit.
The increase in the price of oil shifts the typical firm's cost curves up to MC2 and ATC2, and shifts the industry supply curve up to S2.
The equilibrium price rises from P1 to P2, but the price does not increase by as much as the increase in marginal cost for the firm.
As a result, price is less than average total cost for the firm, so profits are negative.
In the long run, the negative profits lead some firms to exit the industry.
As they do so, the industry-supply curve shifts to the left.
This continues until the price rises to equal the minimum point on the firm's average-total-cost curve.
The long-run equilibrium occurs with supply curve S3, equilibrium price P3, industry output Q3, and firm's output q3.
Thus, in the long run, profits are zero again and there are fewer firms in the industry.
其中的第二段解释我不是很明白，为什么p2达不到p3的水平
谢谢大家
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