A. Any PC running Windows 10 Pro can be upgraded to LTSC with a $99 upgrade pack
B. You must buy a new PC with Win10 LTSC already installed
C. Your organization must buy a Windows Volume License with Software Assurance (or equivalent), after which you can upgrade your previously-licensed machines in place to Win10 LTSC
D. Your organization must buy a Windows Volume License with Software Assurance (or equivalent), after which you must wipe the machine completely in order to install Win10 LTSC
As with any discussion of Microsoft licensing, a degree in Licensology helps, but to a first approximation you need to have a Volume License with Software Assurance in order to run (or even install) an LTSC version of Windows 10. Nowadays, in most cases, for most organizations, that means an Enterprise E3 or E5 subscription.