To ensure that the conclusion of a story maintains consistency with the narrative and aligns with the overall form of the story, the most relevant element would be:
c. The story should have a consistent tone.
A consistent tone throughout the narrative, including the conclusion, helps to create a cohesive reading experience. While internal and external conflicts, characterizations, and the number of characters are important elements in storytelling, maintaining a consistent tone is crucial for unifying the story as a whole.