You need to add a read-only domain controller (RODC) to the forest

Your network contains an Active Directory forest. The forest contains a single domain named
contoso.com. The domain contains domain controllers that run either Windows Server 2003
or Windows Server 2008 R2.
The functional level of the domain and the forest is Windows Server 2003.
You need to add a read-only domain controller (RODC) to the forest.
What should you do first?

A.
Upgrade the domain controllers that run Windows Server 2003.
B.Raise the domain functional level.
C.Run the adprep command.
D.Raise the forest functional level.