A、The early history of bookbinding. B、How old books become valuable. C、Economical ways to protect old books. D、Why some books de

W: Excuse me, I’ve been using this old book for a research project and I noticed that a lot of pages are turning brown and becoming brittle.
M: Yes, unfortunately, that’s a common problem with books made from wood pulp.
W: I suppose to make paper from wood that you have to add a lot of chemicals and acids to make it turn white.
M: Exactly and it’s the acid that eventually eats away　the paper.
W: Oh, that actually make sense, but this book’s not even 75 years old and I’ve seen books in museum that are hundreds of years old and they’re in fine condition.
M: Well, you see, books have been made from wood pulp only since the 1850’s, before that they were mostly made from materials like animals’ skins, and no chemicals were added.
W: It’s a shame those older wood pulp books are going to fall apart some day. Is there anything that can be clone to preserve them?
M: Eh, currently the only way to stop the books from decaying is to remove the binding and treat each page individually to remove the acid.
W: That doesn’t sound very economical.
M: No, it isn’t. It’s not practical to treat a large number of books with this process, so we only try to rescue the most valuable 1st edition books in our collection.
W: Well, thanks for the explanation. I’d better get back to my project.
M: Good luck, and I hope the old book holds long enough for you to finish it.