Answer:
The correct answer is D) Single-member districts
Explanation:
Modern United States politics is dominated by two major parties, The Republicans (also known as the GOP) and the Democrats.
There are numerous independent candidates but in modern history, the president of the country has been selected from either one these parties.
This is not to say that other parties have not tried to develop a following. The most famous example in the 2016 elections was that of the Libertarian party. While it got some press, the party failed to make a national mark.