The answer is c.
You can immediately rule out a because it's not even close. It can't be b or d because it doesn't really give enough information to cause those emotions. In other words it is vague while still peaking the reader's interest, so it mus be mysterious.
#1 A library? The internet?
#2 Search the library catalog, they're typically organized in sections based on genre and then alphabetically (by author name). Or ask a librarian for help.
#3 You'd write the call number.
#4 It's a code that tells you where items are located and tracks the book (like if somebody else has it checked out or not)
#5 Hierarchical structure or faceted classification