Step 1: Define MARC.The question requires the definition of Machine-Readable Cataloging (MARC). MARC is a standard for representing and communicating bibliographic data and related information in a format readable by machines.
Step 2: Analyze the core purpose.The main purpose of MARC is to standardize the format of cataloging information, enabling computers to read, interpret, and exchange it. It structures data about library items (e.g., author, title, publication date, subject headings) into a consistent format. Thus, it serves as a method for the Representation of Bibliographic Information.
Step 3: Evaluate the other options.The remaining options are incorrect. While MARC data can be transmitted online (B), this is not its defining characteristic. Options (C) and (D) are irrelevant to MARC's function.