Consumer Surplus Equals Zero with Horizontal Demand Steps: - Define consumer surplus as the difference between willingness to pay and actual price, represented by the area above price and below demand curve. - Recognize zero surplus occurs when this area vanishes, meaning price equals willingness to pay for every unit consumed. - Examine demand elasticity: perfectly elastic demand is a horizontal line, aligning price exactly with constant willingness to pay. - Rule out supply elasticities, as they affect producer surplus but not the consumer surplus area directly. Why A is correct: - Perfectly elastic demand means the demand curve is horizontal, so price equals the constant marginal benefit for all units, eliminating the triangular surplus area per the surplus formula (∫(D(p) - p) dq = 0). Why the others are wrong: - B: Perfectly inelastic demand is vertical, creating a triangular surplus above price up to maximum willingness to pay. - C: Perfectly elastic supply shifts the supply curve horizontal but leaves consumer surplus intact if demand slopes downward. - D: Perfectly elastic supply doesn't flatten demand; surplus persists with …