Which one of the following statements is true regarding the tax rate structure below? Taxable income Tax liability $ 20,000 $1,500 40,000 7,200 100,000 25,000 Taxpayer A B C The tax rate structure is vertically equitable. The tax rate structure is horizontally equitable. The tax rate structure is neither horizontally nor vertically equitable. The tax rate structure is both horizontally and vertically equitable.