When a decision to replace the defender was already made, and the only remaining question is when to replace, the defender should be kept for another year so long as Select one: a. the depreciation expense for the defender is smaller than the depreciation expense for the challenger b. the after-tax re-sale value of the defender is smaller than the acquisition price of the challenger c. the acquisition price of the challenger is greater than the marginal cost of keeping the defender for another year. d. the marginal cost of keeping the defender for another year is smaller than the annual uniform equivalent cost of the challenger over its economic life. For a stand-alone project, a public project is accepted if its benefit to cost ratio is Select one a greater than one. b. smaller than one smaller than zero. d. greater than zero