Which of the following allows a user to enable XP mode?

Windows Vista Home Premium did not include XP Mode - the feature was not available on any Vista edition.

Windows XP Mode was released by Microsoft as a free add-on specifically for Windows 7 Professional, Enterprise, and Ultimate editions. It used Windows Virtual PC to run a licensed copy of Windows XP SP3 inside a virtual machine, enabling compatibility with older applications that could not run natively on Windows 7. Windows 7 Home Premium and all Windows Vista editions were explicitly excluded from XP Mode support.

Windows 7 Home Premium was specifically excluded from XP Mode support, as Microsoft reserved the feature for higher-tier Windows 7 editions.

Windows Vista Ultimate did not support XP Mode, as the feature was introduced with Windows 7 and was never made available for Vista.