GED prep guides, nursing and other professional exam cliff notes were high on the list of frequently filched books — but so too were graphic novels, library officials said. Book thieves checked out but never returned 70,144 books from Brooklyn Public Library’s 60 cash-strapped branches in 2012, records show. GED prep guides, nursing and other professional exam cliff notes were high on the list of frequently filched books — but so too were graphic novels, library officials said. “Those are always going missing,” a librarian at the Brooklyn Heights branch told the Daily News Thursday.