Writer: I collaborated with another writer on my last book, instead of writing alone as I usually do. Because the book sold so well as a result of this joint effort, I should collaborate with a writer on my next book so that book will sell well too. Which one of the following principles, if valid, most helps to justify the reasoning above? ['Writers who collaborate on books, if they are good writers, usually produce books that sell well.', 'Writers who do not collaborate on books have a smaller chance of writing a book that will sell well.', "If a person's book sells well because of a collaboration, that person's next book will sell well, if he or she collaborates with the same writer.", "If a person's book sells well because of a collaboration, future collaborations on the part of that person will produce other books that sell well."]