The correct answer is A. perfectly elastic demand curve.
A perfectly elastic demand curve is a horizontal line that indicates that the quantity demanded of a good will change infinitely in response to even a small change in price. This is because in perfect competition, there are many firms selling identical products, so each firm has no control over the price of its product. If a firm raises its price, it will lose all of its customers to other firms that are selling the same product at a lower price. Conversely, if a firm lowers its price, it will attract customers from other firms that are
selling the same product at a higher price.A perfectly inelastic demand curve is a vertical line that indicates that the quantity demanded of a good will not change at all in response to a change in price. This is because the good is a necessity, and consumers will buy the same amount of it regardless of the price.
A perfectly elastic supply curve is a horizontal line that
indicates that firms will supply any quantity of a good at a given price. This is because in perfect competition, firms have no costs of production, so they are willing to supply any quantity of the good at the market price.A perfectly inelastic supply curve is a vertical line that indicates that firms will supply a fixed quantity of a good regardless of the price. This is because the good is a scarce resource, and firms cannot produce more of it even if the price is higher.