Which of the following cannot be legally photocopied for educational purposes under fair-use guidelines?

The correct answer pertains to the concept of fair use in educational settings, which allows for certain types of copying under specific conditions. A chapter from a student textbook cannot be legally photocopied for educational purposes under fair-use guidelines because textbooks are typically protected by copyright. This means that copying any significant portion of a textbook could violate copyright laws unless permission is obtained from the publisher or it falls within a stipulated allowance defined by fair use, which does not usually cover entire chapters or significant portions.

The other options are more aligned with fair-use provisions. A worksheet crafted by a teacher is considered original work and may be photocopied for classroom use without copyright issues. A personal letter to a student is also not subject to copyright restrictions in the same way published materials are, as it pertains to personal communication. Lastly, a portion of a public domain book can freely be copied since public domain works are not protected by copyright and can be used without restriction.