Answer:
The correct answer is option B.
Step-by-step explanation:
In a perfectly competitive market, there is a large number of sellers selling homogenous products. Because of a large number of firms selling identical products, no single firm can affect the price and output level in the market.
All the firms are price takers and face a horizontal line demand curve. There is no restriction on the entry and exit of firms in the market. That is why firms earn zero economic profits in the long run.