Your company has an Active Directory Rights Management Services （AD RMS） server. Users have Windows Vista computers. An Active Directory domain is configured at the Windows Server 2003 functional level. You need to configure AD RMS so that users are able to protect their documents. What should you do（）

A. Install the AD RMS client 2.0 on each client computer.
B. Add the RMS service account to the local administrators group on the AD RMS server.
C. Establish an e-mail account in Active Directory Domain Services （AD DS） for each RMS user.
D. Upgrade the Active Directory domain to the functional level of Windows Server 2008.