Your company has an Active Directory domain.    You log on to the domain controller. The Active Directory Schema snap-in is not available in the Microsoft  Management Console （MMC）.    You need to access the Active Directory Schema snap-in.   What should you do（）

• A、Register Schmmgmt.dll.
• B、Log off and log on again by using an account that is a member of the Schema Admins group.
• C、Use the Ntdsutil.exe command to connect to the schema master operations master and open the  schema for writing.
• D、Add the Active Directory Lightweight Directory Services （AD？LDS） role to the domain controller by using Server Manager.