Answer:
The author most likely includes the detail about the stop sign:
C. to highlight that Mooreland is a small and quiet town.
Step-by-step explanation:
"[...] and was the site of the town's only four-way stop sign" is the quote that will help us answer this question. If this is the only four-way stop sign in the whole town, we can safely assume this is the only intersection there is. A town with only one intersection does not have many streets, which means it is certainly very small. Small towns are often very quiet, tranquil places. Therefore, we can safely choose letter C as the reason for the author to include such detail:
C. to highlight that Mooreland is a small and quiet town.