which action should be performed first?

You work as an IT professional in an international company which is named Contoso. Your major job is to translate business goals into technology decisions and plan mid-range to long-term strategies. And you are experienced in network infrastructure, security policy and business continuity. In your company, you are responsible for infrastructure design and global configuration changes.

A server which runs Windows Server 2008 is installed by you.
And it is installed as the first domain controller in an Active Directory forest.
Since you are the technical support, you are required to install another server as a read-only domain controller (RODC).

To achieve the goal, which action should be performed first?

A.
To achieve the goal, adprep /rodcprep should be run.

B.
To achieve the goal, adprep /domainprep /gpprep should be run.

C.
To achieve the goal, the functional level of the forest should be raised to Windows Server 2003.

D.
To achieve the goal, the functional level of the domain should be raised to Windows Server 2008.