The marginal seller is the seller a. for whom the marginal cost of producing one more unit of output is the lowest among all sellers, and the marginal buyer is the buyer for whom the marginal benefit of one more unit of the good is the highest among all buyers. b. who would leave the market first if the price were any lower, and the marginal buyer is the buyer who would leave the market first if the price were any higher. c. who has the largest producer surplus, and the marginal buyer is the buyer who has the largest consumer surplus. d. who supplies the smallest quantity of the good among all sellers, and the marginal buyer is the buyer who demands the smallest quantity of the good among all buyers.