Your network contains a single Active Directory domain. The functional level of the forest is Windows Server 2008. The functional level of the domain is Windows Server 2008 R2. All DNS servers run Windows Server 2008. All domain controllers run Windows Server 2008 R2. You need to ensure that you can enable the Active Directory Recycle Bin. What should you do（）
- AChange the functional level of the forest.
- BChange the functional level of the domain.
- CModify the Active Directory schema.
- DModify the Universal Group Membership Caching settings.