The correct answer is B, infinitely elastic.

Infinitely elasticity implies that if any firm raises the costs of their commodities above the market price, they will sell absolutely nothing. Moreover, in this market, consumers respond highly to the decrease in the prices of the commodities. A slight decrease in the price of a firm leads to an increase in the number of sales. For a company to optimize its profit, it should ensure that it sets prices below the market price. The increased number of sales can lead to economies of scale when products are sold in higher quantities.