Final answer:
A perfectly competitive firm cannot increase its profits by selling an extremely high quantity because it must accept the market price determined by demand and supply.
Step-by-step explanation:
A perfectly competitive firm cannot increase its profits by selling an extremely high quantity because it must accept the price determined by the market demand and supply. In a perfectly competitive market, the firm faces a perfectly elastic demand curve, meaning buyers are willing to buy any number of units at the market price. Therefore, the firm cannot charge a higher price for a higher quantity, as all units will be sold at the same price.