Final answer:
Option D). The best plot development for creating suspense is the narrator being awakened by the noise of unknown strangers in the distance.
Step-by-step explanation:
The plot development that would best create suspense at the point in the story where the narrator is settling down for the night after a long day traveling westward in a wagon train would be D. The noise of unknown strangers in the distance awakens the narrator. This choice introduces an element of the unknown and raises questions about the intentions of the strangers, which can keep readers on edge and eager to find out what happens next.