I managed to find your options somewhere on the Internet: ebooks, hard cover books, mass market books, and paperback books.
I believe the most expensive form of books among these options are hard cover books. First of all, they take longer periods of time to be made; secondly, they need firmer materials because their first page is not easily bent as that in mass market books (which is just a smaller and cheaper version of paperbacks) or ebooks, which are electronic, so it doesn't take a lot of money to make them.
Answer:
I see nothing but facts 100% agree with you
This moon is in outermost of the four large Galilean satellites. Callisto is the most heavily cratered object. Its surface age of about 4 billion years, Callisto has the oldest landscape in the solar system. It also shows a salty oceanic evidence beneath its icy surface
