Final answer:
National political parties are primarily responsible for deciding the party's positions on key issues and coordinating activities and fundraising for presidential candidates, but do not select county party leadership, serve as presidential campaign staff, or elect state convention delegates.
Step-by-step explanation:
At the national level, political parties are primarily responsible for C. deciding the parties positions on key issues. National party organizations play a pivotal role in coordinating activities for elections at the national level, including fundraising and strategy for presidential candidates. They also work closely with the efforts of the House and Senate to promote the party's agendas. It is at the national convention where delegates, chosen from state and local conventions, come together to discuss broader issues and ultimately determine the party's stance on various matters. Though they provide overarching direction, national-level entities do not typically handle local or county leadership selections, operate as campaign staff for presidential candidates, or elect delegates for state conventions; these activities are handled by local and state party organizations respectively.