Concept:A librarian records new books in an official systematic register of library items.
Explanation:A “catalogue” is a complete, organised list of items, usually in alphabetical or systematic order.
In a library, the catalogue contains details of all books available.
“List” is too general and not specific to a library.
A “directory” lists names, addresses, or telephone numbers.
A “roster” is a list of people and their duties or shifts.
Thus, the most suitable word is “catalogue”.
Answer:C. catalogue