How Does the Presidential Primary System Contribute to the Intense

How does the presidential primary system contribute to the intense partisanship of American politics today?

A) It allows minor parties to compete against the major parties, forcing the main parties into extremism.
B) The time leading up to the primaries is intensely competitive, so candidates become more and more extreme.
C) It takes power out of the political parties and puts it into the hands of the candidates, who react by taking their positions to the extreme.
D) The conventions create an artificial emotionalism that appeals to extreme elements.
E) It forces candidates to play the most ideologically extreme elements within their party.