Explanation:

- Monopoly

- In a monopoly, a single firm dominates the market.

- It has a very large degree of control over the price.

- No close substitutes are available.

- Barriers to entry prevent other firms from entering.

- Imperfect Competition

- Multiple firms, each with some control over their prices.

- Products can be differentiated or similar.

- Examples include monopolistic competition and oligopoly.

- Oligopoly

- A small number of firms dominate the market.

- Each firm has significant control over its pricing.

- Firms are interdependent and may collude to set prices.

- Perfect Competition

- Many small firms with no control over prices.

- Products are identical.

- Easy entry and exit from the market.