Final answer:
The primary function of county-level executive committees for political parties is to conduct elections, which includes mobilizing voters, training candidates, and recruiting party members and volunteers.
Step-by-step explanation:
The most important function of county-level executive committees for each political party is B) Conducting elections. These county organizations are crucial for election operations, particularly around election time, taking responsibility for tasks such as identifying and mobilizing voters and donors, training potential candidates, and recruiting new members. They also find volunteers for Election Day to operate polls or monitor the elections, ensuring they are conducted fairly. Additionally, these committees play a role in strategy coordination and supporting party candidates, especially for local county and city offices.