Answer:
D.) all citizens of Westport County
Step-by-step explanation:
The explanation for this answer is extremely easy and is described in the last paragraph of the text. This is because it is in this paragraph that the author says that the letter was made to ask that all citizens of the county of Westport vote "No" on Proposition S. For this reason, we can see that the letter has as target audience all citizens of Westport County
The part of the letter that makes this clear is: "...I am proud to join my fellow residents of Northfield in urging all citizens of Westport County to vote No on Proposition S in the upcoming election. What is good for Northfield is good for all of Westport County."