Statistics from the National Booksellers Association indicate that during the last five years most bookstores have started to experience declining revenues from the sale of fiction, despite national campaigns to encourage people to read more fiction. Ttherefore, these reading campaigns have been largely unsuccessful. Which one of the following statements, if true, most seriously weakens the argument? ['The National Booksellers Association statistics do not include profits from selling novels by mail to overseas customers.', 'During the last five years the most profitable items in bookstores have been newspapers and periodicals rather than novels.', 'Due to the poor economic conditions that have prevailed during the last five years, most libraries report substantial increases in the number of patrons seeking books on changing careers and starting new businesses.', 'Mail order book clubs have enjoyed substantial growth in fiction sales throughout the last five years.']