The correct answer is B. A two-party system.
Nowadays the U.S. political system is a two party system: Democratic Party and Republican Party. Since 1852, both parties have shared the power in the U.S.
Of the 50 states, in 48, presidential candidates get all of a state’s electoral as long as they win a plurality of the vote in that state. Candidates who run for Congress need to obtain a plurality –majority of the vote- to win the elction.