Final answer:
National party organizations primarily play an advisory role to congressional candidates, offering strategic advice and resources, though they also may provide financial support and have some involvement in the nomination process.
Step-by-step explanation:
The function that the national party organizations perform in relation to congressional candidates can best be described as a B) Advisory role. National party organizations, like the Democratic National Committee (DNC) or the Republican National Committee (RNC), provide strategic advice, coordination, and resources to candidates. While they may also offer financial support, their control is not direct as candidates generally control their own campaigns. Additionally, while the national party organizations do play a role in the nomination process, the selection of candidates typically occurs at the state and local level through primaries and caucuses.