One state adds a 7 percent sales tax to the price of most products purchased within its jurisdiction. This tax, therefore, if viewed as tax on income, has the reverse effect of the federal income tax: the lower the income, the higher the annual percentage rate at which the income is taxed.

The conclusion above would be properly drawn if which of the following were assumed as a premise?

(A) The amount of money citizens spend on products subject to the state tax tends to be equal across income levels.

(B) The federal income tax favors citizens with high incomes, whereas the state sales tax favors citizens with low incomes.

(C) Citizens with low annual incomes can afford to pay a relatively higher percentage of their incomes in state sales tax, since their federal income tax is relatively low.

(D) The lower a state’s sales tax, the more it will tend to redistribute income from the more affluent citizens to the rest of society.（A）

(E) Citizens who fail to earn federally taxable income are also exempt from the state sales tax.

请问这句话该怎么理解啊:

This tax, therefore, if viewed as tax on income, has the reverse effect of the federal income tax:

This sentence suggests that if you look at this tax as a tax on income (like income tax), it has the opposition effect of federal tax. Federal tax works in a way that the higher the income is, the higher the tax rate is. The sales tax is opposite: the lower the income, the higher the tax rate (because the 7% is on the goods purchased and steady).

對此題的assumption還是不清楚如何得出

我知道 poor: (income tas+ sales tax)/income > rich (income tax+ sales tax)/ income

但為何需要A這個前提?

另外 如何用"取非" 來驗證?