Which of the following BEST describes the concept of right to downgrade?

A. It allows for the return of a new OS license if the newer OS is not compatible with the currently installed software and is returning to the previously used OS
B. It allows a server to run on fewer resources than what is outlined in the minimum requirements document without purchasing a license
C. It allows for a previous version of an OS to be deployed in a test environment for each current license that is purchased
D. It allows a previous version of an OS to be installed and covered by the same license as the newer version