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（）

You have an Active Directory domain that runs Windows Server 2008 R2. You need to implement  a certification authority （CA） server that meets the following requirements：    
- Allows the certification authority to automatically issue certificates  - Integrates with Active Directory Domain Services    
What should you do（）