The total revenue generated by a perfectly competitive firm:

In a perfectly competitive market, each firm is a price taker, meaning that the price of the product is determined by the overall market and not by individual firms. When a perfectly competitive firm increases its output, it can sell each additional unit at the market-determined price. Since the firm can sell as many units as it wants at this price without affecting the market price, the total revenue generated increases by a constant amount for each additional unit sold.

This constant increase in total revenue occurs because the price remains the same regardless of the quantity produced, making the firm's marginal revenue equal to the price of the product. Therefore, for every additional unit the firm sells, it earns the same amount of money—equal to the price of the product. This is the fundamental reason why total revenue increases linearly with output in perfect competition.

As such, the option indicating that total revenue increases by a constant amount as output increases accurately reflects the behavior of revenue in a perfectly competitive market.