- Upgrading the operating system
- Reinstalling an application that is not functioning correctly
- Restoring a volume from a backup set
- Defragmenting a hard-drive volume
The correct answer is 4.
Preventative maintenance (PM) seeks to proactively treat a component or system before it fails, in an effort to prolong the time before actual failure. Among the options, only defragmentation is a software form of PM. Upgrading the operating system is not the same as updating it, which would be a form of PM. The remaining two options are reactive, rather than proactive.
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