Answer:
B. Word count
Step-by-step explanation:
Word count has nothing to do with the author's purpose whereas tone is used to tell the reader the author's attitude towards the subject (a clue for determining the author's purpose), intended audience is used to tell the reader who the author intended to write the story for (a clue for determining the author's purpose), and word choice can be used to find countless meanings in the text (a clue for determining the author's purpose). Hope I didn't make that too confusing, haha!