What should you identify?

Your network contains an Active Directory forest. The forest contains two Active Directory
domains named contoso.com and child.contoso.com. The forest functional level is Windows
Server 2003. The functional level of both domains is Windows Server 2008.
The forest contains three domain controllers. The domain controllers are configured as
shown in the following table.

DC1 and DC2 have the DNS Server server role installed and are authoritative for both
contoso.com and child.contoso.com.
The child.contoso.com domain contains a server named serverl.child.contoso.com that runs
Windows Server 2012.
You plan to deploy server1.child.contoso.com as a read-only domain controller (RODC).
You run the adprep.exe /rodcprep command on DC3 and receive the following error message:

You need to identify what prevents you from successfully running Adprep /rodcprep on DC3.
What should you identify?

A.
The domain functional level of child.contoso.com is set to the wrong level.

B.
DC3 cannot connect to the infrastructure master on DC2.

C.
DC3 cannot connect to the domain naming master on DC1.

D.
The forest functional level is set to the wrong level.