Which of the following is the minimum domain functional level required before you can promote a
member server running Windows Server 2012 R2 so that it functions as a domain controller?
A.
Windows Server 2003
B.
Windows Server 2008
C.
Windows Server 2008 R2
D.
Windows Server 2012
https://technet.microsoft.com/en-us/library/understanding-active-directory-functional-levels(v=ws.10).aspx
Forest functional level:
Windows Server 2003
Supported domain controllers:
Windows Server 2012 R2
Windows Server 2012
Windows Server 2008 R2
Windows Server 2008
Windows Server 2003