D. Unit-demand consumers: There are "n" consumers. Each consumer has an index formula_54. There is a single type of good. Each consumer formula_5 wants at most a single unit of the good, which gives him a utility of formula_56. The consumers are ordered such that formula_57 is a weakly increasing function of formula_5. If the supply is formula_59 units, then any price formula_60 satisfying formula_61 is an equilibrium price, since there are "k" consumers that either want to buy the product or indifferent between buying and not buying it. Note that an increase in supply causes a decrease in price.