Answer:
The rhetorical appeal that this sentence uses is B. Pathos
Step-by-step explanation:
Pathos is focused on causing feelings, sadness or sympathy towards the topic or person that is being mentioned. In this specific sentence "As the former treasurer and current mayor of this town, I wholeheartedly support the plan to build the new library." the use of the word wholeheartedly is adding a deeply emotional shade to the message, besides since he uses his position as an active member in the developing of the town he connect with the memories and feelings of the people.