Marginal costs facing any firm considering a change in output represent:

a. extraordinary overtime charges that must sometimes be paid to increase output. b. the cost incurred even if the firm produces zero output. c. the difference between the total cost actually incurred to produce any given output and the smallest possible total cost of producing that output. d. the increase in total cost that accrues from a 1-unit increase in quantity produced. e. the increase in total cost that accrues from any increase in quantity produced, whether 1 unit or more