Short run supply curve of a perfectly competitive firm is that portion of marginal cost curve which is above average variable cost curve. According to C.E. Ferguson, “The short run supply curve of a firm in perfect competition is precisely its Marginal Cost Curve for all rates of output equal to or greater than the rate of output associated with minimum average variable cost.”

The correct answer is option 'D', which states that a purely competitive firm's supply schedule in the short run is determined by its marginal cost curve.

In order to understand why this is the correct answer, let's break down the components of the question and examine them individually.

- Average revenue: Average revenue is the total revenue divided by the quantity sold. While it is an important factor for a firm to consider, it does not directly determine the firm's supply schedule. Average revenue is influenced by the demand for the firm's product, but it does not determine the firm's production decisions.

- Marginal revenue: Marginal revenue is the change in total revenue that results from selling one additional unit of output. It is derived from the demand curve and represents the additional revenue a firm earns from selling one more unit. While marginal revenue is an important factor for a firm to consider, it also does not directly determine the firm's supply schedule. Marginal revenue helps a firm determine the optimal level of production, but it does not determine the firm's actual production decisions.

- Marginal utility for money curve: The marginal utility for money curve is a concept from consumer theory and represents the additional satisfaction or utility a consumer derives from spending one more unit of money on a particular good. This concept is not directly applicable to a firm's supply decisions. Firms are motivated by profit maximization, not by maximizing their own utility or satisfaction.

- Marginal cost curve: The marginal cost curve represents the additional cost a firm incurs from producing one more unit of output. It is derived from the firm's production function and reflects the firm's cost structure. The marginal cost curve directly determines a firm's supply schedule in the short run. As long as the price of the product is equal to or greater than the marginal cost of production, the firm will continue to produce and supply the product. The firm will only stop producing when the price falls below the marginal cost, as it would result in losses.

In summary, a purely competitive firm's supply schedule in the short run is determined by its marginal cost curve. The firm will produce and supply the product as long as the price is equal to or greater than the marginal cost of production. The firm's production decisions are driven by profit maximization, and the marginal cost curve reflects the cost structure of the firm.