The correct answer is c) oligopoly.
The automobile industry is mostly associated with an oligopoly.
When a market is controlled by just a few numbers of companies, but none of them is above the others, we are talking about an oligopoly. The can collude intentionally or not, to establish prizes and to not let other companies compete with them.
In the United States, the automobile companies are a good example of an oligopoly. Basically, just three companies control the production and selling of American cars: Ford, General Motors, and Chrysler. They can determine prices and the models that will be in the market.