Huck's reference to Mark Twain being the author of The Adventures of Tom Sawyer adds to the text mainly by

A. confusing the reader and bringing doubt about who is truly writing this book
B. bringing some humor and giving Huck added credibility as a narrator
C. establishing that the events of Tom Sawyer were made up and Huck is going to tell what really happened
O D. alerting the reader that this book is not a novel, but an autobiography