Final answer:
To convert a GUI server to Server Core on Windows Server 2012 R2, use PowerShell to uninstall the GUI features.
Step-by-step explanation:
The best answer to convert a GUI server to Server Core on Windows Server 2012 R2 is b) Use PowerShell to uninstall the GUI features.
To convert a GUI server to Server Core using PowerShell, follow these steps:
1. Open PowerShell as an administrator.
2. Run the command Uninstall-WindowsFeature Server-Gui-Shell, Server-Gui-Mgmt-Infra to uninstall the GUI features.
3. Restart the server to complete the conversion.
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