A library's online catalog is a computerized index of

Abooks found within the library.
Blibrary staff contact numbers.
Csearch engines offered by the library.
Dlibrary members.

Verified Answer :

A. Books found within the library.

The correct answer is A: Books found within the library.

This is so because the purpose of a library's online catalog is to provide the full stock of the physical library, including not only books but also all the written material and multimedia files in it, as well as their locations and elements (such as author, title, subject, bibliography, etc.), in order to locate them quickly and use them.