City A sells more books than City B, so residents in City A are more likely to read than residents in City B. Which of the following will weaken the above conclusions? ['y A. has more population than city B.', 'There are many residents in city B who buy books in city A.', 'B residents are accustomed to borrowing books from the library.', 'The average selling price of books in D. A is slightly higher than in B.']