Answer:
The correct answer is option d.
Explanation:
The firms in a perfectly competitive market are price takers. The price taker firms do not determine their product prices. The price of a product is determined through the market forces by the equalisation of demand and supply.
The firms face a horizontal line demand curve at the level of market price.
There are large number of sellers selling identical products in the market, so if a firm increases its price, the buyers will go somewhere else where the price is lower.