你说的1和2是对的。但总的来说，这个框架不适合讨论产业结构的演化问题。

比如，关于3，瞬间调整的话，也可以说一开始市场上就达到最优企业数量，每个企业在LAC最低点生产，市场达到供求均衡，既没有企业退出，也没有新企业进入。

有调整时间就更不好分析了，这是一个静态的框架。

谢谢版主指点

现在对静态框架的局限有了新的认识了

For 1)2) basically you are right. It's a basic assumption on competitive equilibrium, which is all firms are identical and have the same cost function. In the long run, each firm can access to the most efficient production technology. For 3)in the long run, the firms only getting strictly negative profits will quit. They quit not because they couldn't adjust their output, but because the market price is bigger than their mininum average costs, which is decided by their cost functions ( technology, input....)