Final answer:
Modeling how to read the texts chosen for students helps demonstrate fluent reading behaviors, which is most effective for enhancing students' reading fluency.
Step-by-step explanation:
To facilitate reading fluency among students, the most effective change to the described activity would be C. modeling how to read the selected texts before asking the students to read them. This approach provides students with a clear example of fluent reading, including appropriate pacing, phrasing, and expression.
Modeling reading behaviors can have a positive impact by demonstrating what fluent reading sounds like, allowing students to mirror these skills during their own reading. Introducing texts that can be read with 100 percent accuracy or choosing only fiction or nonfiction may not necessarily influence fluency directly, and while introducing key vocabulary can support comprehension, it does not directly address fluency as effectively as live modeling.