Which of the following is a correct conclusion regarding the successful implementation of fiscal policy? a. Successful fiscal policy is much easier to achieve today because econometric models make economic forecasting much easier. b. As the income-expenditure model suggests, fiscal policy planners can move GDP to any level they please by changing tax and spending levels. TO c. Successful fiscal policy is difficult to achieve because in the real world the investment, net exports, and consumption schedules are constantly shifting d. Successful fiscal policy would be easy to achieve it Congress would stay out of the economy and permit natural market forces to restore full-employment equilibrium.