In everyday usage, which of the following is something that every physical book must have by definition?

Introduction / Context:
This logical reasoning and general knowledge question asks you to think carefully about what defines a physical book. Many items such as novels, textbooks, and picture books share some common features, but not all books have exactly the same parts. The question helps you distinguish between features that are optional and features that are absolutely necessary for something to be called a book.

Given Data / Assumptions:

• The options list common parts of books: preface, text, index, and pages.
• The question is about what a physical book always has, not what it usually or often has.
• The word book refers to a bound collection of sheets, not to an electronic e book or audio book.

Concept / Approach:
By definition, a physical book is a collection of written, printed, or illustrated sheets of paper (or similar material) that are bound together along one edge, forming pages that can be turned. Some books have mainly text, some have pictures, and some have a mixture. A preface is an introductory section written by the author or editor, but many small books or simple storybooks do not have a preface. An index is a list at the end that helps readers find topics by page number; however, novels and many simple books do not include an index. The content of a book can be text, images, or both, so it is not accurate to say that printed words must be present on every page. The only feature that every physical book must have is at least one page or set of pages that are bound together, because without pages there is nothing to read or turn.

Step-by-Step Solution:

Verification / Alternative check:
Definitions in dictionaries describe a book as a written or printed work consisting of pages glued or sewn together along one side and bound in covers. They focus on the idea of multiple pages forming a volume. They do not require that every book contain a preface, index, or specific type of content. Library classification systems also treat books as physical volumes, sometimes containing mostly images, diagrams, or music notation. These references support the conclusion that pages and binding are essential features of a physical book, while prefaces and indexes are optional parts.

Why Other Options Are Wrong:

A preface written by the author at the beginning is wrong because many books, especially simple storybooks or manuals, have no preface at all.

Printed words as text on every single page is incorrect because picture books or art books can have pages with images only, and the definition of a book does not demand text on every page.

An index at the back listing topics and page numbers is wrong because indexes are mainly used in reference works, textbooks, and some non fiction, but are absent in a large number of books.

Common Pitfalls:
Students may focus on what they usually see in textbooks, which often contain prefaces, indexes, and lots of text, and then assume these features are universal. Another pitfall is forgetting category exceptions, such as picture books or comics that are still books but do not follow textbook structure. To avoid these mistakes, concentrate on the core definition: a physical book must have pages bound together; other parts like prefaces and indexes are useful but optional.