Which of the following is not a feature of a book?

The reason the table of contents is identified as not a feature of a book is that it is specifically an element characteristic of the organization within a non-fiction or instructional book, often providing a roadmap for the content within. However, the front cover, back cover, and the way a book is physically stored relate to the book's physicality and overall presentation. The front cover serves to attract attention and give information about the book, while the back cover may provide additional details such as a summary or author information. How a book is stored pertains to its treatment and physical care, which is also relevant to the concept of a book. Thus, the table of contents distinguishes itself as part of the structure of some books, but not a universal feature across all books.