What should you do?

You are an enterprise administrator for Domain.com. The company currently has a Windows Server 2003 R2 domain running on the network.
You want to install a read-only domain controller into the structure of your Directory Services. You want to accomplish this without upgrading your domain to Windows Server 2008 Directory Services. You thus have to determine a way to add RODC on your network. What should you do?

A.
You need to change the forest functional level to Windows Server 2008 mixed mode.

B.
You need to run adprep on a Windows Server 2003 R2 domain controller.

C.
You need to upgrade the domain to a Windows Server 2008 Directory Services domain.

D.
You need to change the domain functional level to Windows Server 2008 mixed mode.

Explanation:
The scenario can be accomplished by running adprep on a Windows Server 2003 R2 domain controller by using Windows Server 2008 media.
Reference : Syngress.The.Real.MCTS.MCITP.Exam.70-648.Prep.Kit.Mar.2008 Section 4, Configure Active Directory Federation Services (AD FS) (13 Questions)