Explanation:

- Antivirus: This is a utility software. It protects your computer from malicious activities and software like viruses and malware.

- Firewalls: Another type of utility software. Firewalls help secure a network by controlling inbound and outbound traffic.

- Disk defragmenter: Also utility software. It reorganizes fragmented data to improve system efficiency.

- MS-DOS: This is an operating system, not a utility software. MS-DOS stands for Microsoft Disk Operating System and provides an interface between hardware and software.

Correct Answer:

- MS-DOS

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