In each of the following situations, do you think the industry described will be perfectly competitive or not? Explain your answer.

a. There are two producers of aluminum in the world, a good sold in many places.

b. The price of natural gas is determined by global supply and demand. A small share of that global supply is produced by a handful of companies located in the North Sea.

c. Dozens of designers sell high-fashion clothes. Each designer has a distinctive style and a loyal clientele.

d. There are many baseball teams in the United States, one or two in each major city and each selling tickets to its hometown events.