Which of the following should be made only when warranted by evaluation?

Revisions should be made only when warranted by evaluation because they are significant changes that may affect the overall content or structure of the material being taught. When an evaluation indicates that certain aspects of the instruction are not meeting objectives or resonating with learners, it is essential to analyze those findings before implementing any major changes. This ensures that the revisions are grounded in concrete data and feedback, leading to more effective training outcomes.

Other options, like materials and modifications, may occur more frequently and can be adjusted as needed based on ongoing observations or immediate feedback. Evaluations, while crucial to the process, are the tools used to determine whether revisions are necessary; therefore, they do not directly lead to change but rather inform it.