Premise: The question stated that state added a tax based on their discretion.
Conclusion: When it's counted into federal tax, it makes the lower income people pay more taxes bcs the % of their taxed income is higher comparing with higher income people.
(A) The amount of money citizens spend on products subject to the state tax tends to be equal across income levels. -- Yes, or else it would not make the lower income people pay more taxes when it counts into the ttl income
(B) The federal income tax favors citizens with high incomes, whereas the state sales tax favors citizens with low incomes. -- No, the reverse, coz it's stated as a conclusion/result the rich is favored instead.
(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. --No, federal income tax is low is not given and irrelevant to the reasoning
(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. -- No, not relation is stated between state tax and wealth distribution
(E) Citizens who fail to earn federally taxable income are also exempt from the state sales tax. --No, nothing related to exemption was mentioned.