Your network contains one Active Directory domain named contoso.com. The domain contains the domain
controllers configured as shown in the following table.

The functional level of the domain and the forest is Windows Server 2008.
An administrator named Admin1 is a member of the Domain Admins group.
You need to ensure that Admin1 can deploy a Windows Server 2012 R2 domain controller to contoso.com.
What should you do?

A.
Raise the forest functional level.

B.
Run the Set-ADForestMode cmdlet.

C.
Raise the domain functional level.

D.
Run the adprep.exe command.

Explanation:
Adprep.exe commands run automatically as needed as part of the AD DS installation process on servers that
run Windows Server 2012 or later. The commands need to run in the following cases:
* Before you add the first domain controller that runs a version of Windows Server that is later than the latest
version that is running in your existing domain.
* Before you upgrade an existing domain controller to a later version of Windows Server, if that domain
controller will be the first domain controller in the domain or forest to run that version of Windows Server.
Running Adprep.exe
https://technet.microsoft.com/en-us/library/dd464018(v=ws.10).aspx