Which market structure has a single company can or seller in a market with many barriers to entry

The question is asking which market structure has a single company or seller in a market with many barriers to entry and the answer is C. Monopoly. A monopoly is a situation where only one company has a chance to sell their products. Think for example about a national post company that is the only company that has the right to enter people's houses and access their mailbox - this is an example of a monopoly.