Happy to help! Let's take a look at the stimulus before we dive into the answer choices.
The stimulus concludes that people are making exaggerated predictions of the future when they say that printed books will soon be replaced by electronic formats in libraries. The stimulus reasons that because book stores and public libraries will stock books in the format the public wants, printed books will still be around.
The question stem is asking us to pick an answer that strengthens the argument.
The stimulus tells us that the general public will keep on wanting printed books. We're also told that public libraries will continue to stock books in the format the public wants. But what if the new electronic formats made printing books economically inefficient (because you could get the exact same book for way cheaper in an electronic format)? The argument assumes that this isn't the case. If we can find an answer choice that provides support for this assumption, then we can strengthen the argument.
(B) says, "Publishers will continue to print books in the format stocked by bookstores and public libraries."
This answer choice does a great job in matching the anticipation we made before looking at the answers. Obviously, a publisher must print a book in order for someone to be able to read a printed book. If it's true that the public will continue wanting printed books AND that publishing companies will continue to print books, then this strengthens the argument and its conclusion that predictions that printed books will soon be replaced by books in electronic formats such as CD-Rom are exaggerated.
Does this make sense? Let us know if you have any more questions!