Answer:
Oligopoly
Step-by-step explanation:
An oligopoly can be defined as a market structure comprising of a small number of firms (sellers) offering identical or similar products, wherein none can limit the significant influence of others.
Hence, it is a market structure that is distinguished by several characteristics, one of which is either similar or identical products and dominance by few firms.
The characteristics of an oligopolistic market structure are;
I. Mutual interdependence between the firms.
II. It's a market that is typically controlled by many small firms.
III. Difficult entry to new firms.
In this scenario, four major breakfast cereal companies share a majority of the cereal market (identical or similar products) such as Kellogg, Post, General Mills, and Quaker. Thus, this is an example of an oligopoly.