Final answer:
Modern nominating conventions are different because the nominee is generally known before the convention, due to the primary system. The conventions now serve to promote and unify the party around the chosen candidate for the general election. Therefore the correct answer is a.the nominee is typically already known at that point
Step-by-step explanation:
Modern nominating conventions differ from their predecessors in that the nominee is typically already known at that point. The rise of the presidential primary and caucus system has led to conventions becoming events to showcase and promote the chosen candidate, who has often been predetermined by the primary elections. The drama and uncertainty that once characterized the conventions have largely disappeared, with the conventions now serving as a platform for party unity and launching the general election campaign.