According to Its Proponents, Which of the Following Is a Benefit

According to its proponents, which of the following is a benefit of the proposed national sales tax?

A) Higher-income people would receive a rebate check at the beginning of each month to put toward their retirement.
B) Those involved in illegal business activities would make a greater contribution to the legitimate economy through spending.
C) The sales tax would, by its nature, be flat.
D) The tax would be modestly progressive.