The correct answer for this question is option 4, Perfect competition.

Perfect competition is a market structure characterized by a large number of firms, all producing identical or homogeneous products or services. In such a market, individual firms have no control over the price of their products, as they are price takers. This means that they have to accept the prevailing market price and cannot independently set higher prices.

In a perfectly competitive market, the demand for the product is considered to have infinite elasticity, meaning that consumers are highly sensitive to even the slightest changes in price. This means that firms cannot increase prices without losing customers, as there are numerous other firms offering similar products at the prevailing market price.

Option 1, Oligopoly, refers to a market structure where a small number of firms dominate the market. Option 2, Imperfect competition, refers to markets that do not meet the criteria of perfect competition, such as having differentiated products or some control over price. Option 3, Monopolistic competition, refers to a market structure where there are many firms selling differentiated products.

Therefore, option 4, Perfect competition, accurately describes the market structure described in the question.