The correct answer is C) Political parties.
Though not mentioned in the US Constitution, political parties play a direct role in the US government through Congressional discourse and establishing specific political platforms.
Political parties are organizations that have platforms in which they define the type of government they aspire for the country and the way to reach the goals established in their plans and programs. People are free to vote for the party and the candidate they want. In the United States, the Democratic party and the Republican Party have shared the presidency since the very beginning of the nation.