The answer is C: a statement of the author’s purpose in writing the book, which may include suggestions for using the book.
A preface is an introduction to a book written by the author of the book. A preface usually includes the story of how the book came to being —this includes the author´s purpose in writing the book—, the ideas that cemented its development, and, finally, they usually include acknowledgements to the people or institutions that helped the project come to a conclusion. The preface is usually signed, and following the signature the date and place of writing is included.
