The total gains from trade within a price system is Select one: A. the area beneath the market demand curve and above the market clearing price minus the area beneath the market supply curve and beneath the market clearing price. B. always equal to zero. C. the area beneath the market supply curve and above the market clearing price plus the area above the market demand curve and beneath the market clearing price. D. the area beneath the market demand curve and above the market clearing price plus the area above the market supply curve and beneath the market clearing price