Which of the following is the best example of core system software?

Correct answer: Operating System.

Core system software manages the computer hardware and provides services for application programs. An operating system is the primary example because it manages memory, processors, files, devices, and user interaction.

Antivirus software is a utility program and may be grouped under system utilities in a broad classification, but it is not the best example of core system software. Oracle and MS Word are application software.