In a recent benefit-cost analysis of a proposed regulation that generated positive net benefits in the present but negative net benefits in the future, the government used a 5% social discount rate. If it had instead used a 4% social discount rate, the net present value of the policy would have been ______; if it had used a 6% social discount rate, the net present value would have been ______. Select one: a. higher; higher. b. higher; lower. c. lower; higher. d. lower; lower.