D is the answer. It suggests that there are books which library users need that can only be found in hardcover, so buying only paperback books will not be feasible.
Option A is not relevant since it applies to all type of books.
Option B and C strengthen the argument to buy only paperback books.
Option E is irrelevant since it talks about the public users propensity to buy books which does not relate to the argument.
Paperback books wear out more quickly than hardcover books do, but paperback books cost much less. Therefore, users of public libraries would be better served if public libraries bought only paperback books, since by so doing these libraries could increase the number of new book titles added to their collections without increasing their budgets.
Which one of the following, if true, most seriously weakens the argument?
(A) If a public library’s overall budget is cut, the budge for new acquisitions is usually cut back more than is that for day-to-day operations
(B) Paperback books can very inexpensively have their covers reinforced in order to make them last longer
(C) Many paperback books are never published in hardcover
(D) Library users as a group depend on their public library for access to a wide variety of up-to-date reference books that are published in hardcover only
(E) People are more likely to buy for themselves a copy of a book they had previously borrowed from the publish library if that book is available in paperback