Answer:If the demand curve and the marginal revenue curve weren't the same curve for a perfectly competitive firm, then the firm would not be resource-allocative efficient.
Explanation: Demand curve is a graphical representation of the rate of change of demand as the price of a product changes.
Marginal revenue curve is a graphical representation of the rate of change of marginal revenueas the production and the quantity of output produced changes.
For a perfectly competitive firm with no market control, the marginal revenue curve is a horizontal line.
FOR A PERFECTLY COMPETITIVE FIRM THE MARGINAL REVENUE CURVE AND THE DEMAND CURVE SHOULD BE THE SAME IF THE FIRM ALLOCATES ITS RESOURCES EFFICIENTLY.