Your network contains an Active Directory forest named contoso.com. The contoso.com domain only contains domain controllers that run Windows Server 2012
The forest contains a child domain named child.contoso.com. The child.contoso.com domain only contains domain controllers that run Windows Server 2008 R2
Service Pack 1 (SP1). The child.contoso.com domain contains a member server named Server1 that runs Windows Server 2012 R2.
You have access to four administrative user accounts in the forest. The administrative user accounts are configured as shown in the following table.
You need to ensure that you can add a domain controller that runs Windows Server 2012 R2 to the child.contoso.com domain.
Which account should you use to run adprep.exe?
Adprep.exe performs operations that must be completed on the domain controllers that run in an existing Active Directory environment before you can add a
domain controller that runs that version of Windows Server.
Preparing to run adprep /domainprep (see step 2 below).
To help ensure that the adprep /domainprep command runs successfully, complete these steps before you run the command on the infrastructure operations
master role holder in each domain:
1. Make sure that the schema updates that adprep /forestprep performs replicated throughout the forest or that they at least replicated to the infrastructure master
for the domain where you plan to run adprep /domainprep.
2. Make sure that you can log on to the infrastructure master with an account that is a member of the Domain Admins group.
3. Verify that the domain functional level is appropriate.
References: Running Adprep.exe