In Today's American Society, What Is the Primary Purpose of the National

In today's American society, what is the primary purpose of the national party conventions that are held in the summer prior to the presidential elections?

A) To showcase the party's presidential candidate and garner momentum for the upcoming election
B) To interview and narrow the field of candidates for the upcoming primary elections
C) To appoint cabinet members and other officeholders in case the party's candidate wins the election
D) To seek balance and a cooperative spirit between the two major parties on major issues prior to the election
E) To introduce new legislation to Congress in order to satisfy campaign promises