What is the criteria for a school district to remove a book according to the case involving "Annie on my Mind"?

The correct choice highlights the importance of educational suitability as the primary criterion for removing a book from a school district's library or curriculum. The backdrop of the case involving "Annie on My Mind" revolves around the educational value that a book holds, particularly when it comes to addressing issues of sexual identity and diversity.

Educational suitability means that books should contribute positively to the educational experience of students. If a book is deemed not to serve this purpose—whether due to its content being inappropriate for the targeted age group, or failing to meet curricular standards—it may be subject to removal. This reflects a broader concern within educational settings to ensure that all materials are not only age-appropriate but also beneficial to students' intellectual and emotional growth.

In the context of the other options, while community opinions can influence decisions about book removal, they do not serve as a formal criterion on their own without educational justification. Simply stating that all books should remain regardless of content overlooks the need for materials to align with educational objectives. Lastly, stating that books can only be removed if they are illegal does not accurately reflect the nuanced criteria that school districts utilize, which is more focused on appropriateness and suitability for the educational setting than on legality alone.