One purpose of a presidential primary to choose delegates for the national convention.
Answer: Option A
Explanation:
An election in the U.S.A starts with a lot of candidates and eventually narrows down to just a handful of candidates. The presidential primary plays an important role in this process of finding eligible candidates and nominate them for the next stage of filtering.
In this process, the people who are eligible to vote can choose their preferential candidate from the parties. Although this process is carried out in the local levels too the primary focus is towards the presidential level.