The correct answer is c) people with higher incomes have gained a larger share of wealth. The disparities have increased due to globalization, the unfair distribution of taxing among rich people and middle class and poor people. It is believed by experts (Bairoch, P., 1981) also that, the lack of transparency in the government debt, the policy based not in social justice but inconvenience and in favor of the fewer (richer) over the whole (the middle and poor ones) are all reasons why in the U.S. economy (as well as many occidental countries) the gap between rich and poor is now more evident.
Reference
Bairoch, P. (1981). The main trends in national economic disparities since the industrial revolution. In Disparities in economic development since the Industrial Revolution (pp. 3-17). Palgrave Macmilla