Which of the following statements is true about supply-side economics?

Which of the following statements is true about supply-side economics?

       a.  The main change made by the tax laws of 1981 and 1986 was to 

            increase marginal tax rates in order to balance the budget

       b.  The Laffer Curve says that, if marginal tax rates fall, tax

            revenues will rise, and the budget deficit will decrease

c. If the tax laws of 1981 and 1986 had had their intended effect, consumption would have

risen, causing an increase in both real GDP and in the price level           

       d.  All of the above