Your company has an Active Directory forest. You plan to install an Enterprise certification  authority （CA） on a dedicated stand-alone server. When you attempt to add the Active Directory Certificate Services （AD CS） server role， you find  that the Enterprise CA option is not available. You need to install the AD CS server role as an Enterprise CA.     What should you do first（）

• A、Add the DNS Server server role.
• B、Join the server to the domain.
• C、Add the Web Server （IIS） server role and the AD CS server role.
• D、Add the Active Directory Lightweight Directory Services （AD LDS） server role.