Bookstore owner: Consumers should buy books only from an independent bookstore, not from a bookstore that belongs to a bookstore chain. An independent bookstore tends to carry a much wider variety of books than does a chain bookstore, so because chains often threaten the existence of independent bookstores, they tend to reduce the variety of books available to consumers. Which one of the following principles, if valid, most helps to justify the bookstore owner's argumentation? ['Consumers should not make purchases from any bookstore that deliberately forces competing bookstores out of business.', 'If consumers have no access to any independent bookstore, they should buy books from the chain bookstore with the greatest diversity of books.', 'Consumers should buy books from only those bookstores whose existence does not tend to reduce the variety of books available to consumers.', 'The best interest of the bookselling business is not served when consumers purchase books from businesses whose existence tends to reduce the variety of books available to consumers.']