"<span>a. They perform the most essential tasks" would be the best option from the list, since it is the volunteers who are responsible for organizing the grassroots voters to act. </span>
I believe the answer is: A. They perform the most essential tasks.
In a political party organizational pyramid, you would be placed lower in the pyramid as you made more interactions with potential voters.
Volunteers are the one that made the most interaction such as calling many numbers to ask for donation, spreading gifts and merchandise, organizing marches to support a certain representatives, etc.
