Your network contains a single Active Directory domain.
The functional levelof the forestis Windows Server 2008.
The functional levelof the domainis Windows Server 2008 R2.
All DNS serversrun Windows Server 2008.
All domain controllersrun Windows Server 2008 R2.
You need to ensure that you can enable the Active Directory Recycle Bin.
What should you do?

A.
Change the functional level of the forest.

B.
Change the functional level of the domain.

C.
Modify the Active Directory schema.

D.
Modify the Universal Group Membership Caching settings.

Explanation:
Reference:
http://technet.microsoft.com/en-us/library/dd392261.aspx
Active Directory Recycle Bin Step-by-Step Guide
By default, Active Directory Recycle Bin in WindowsServer 2008 R2 is disabled. To enable it, you must first
raise the forest functional level of your AD DS or AD LDS environment to Windows Server 2008 R2,
which in turn requires all forest domain controllers or all servers that host instances of AD LDS configuration
sets to be running Windows Server 2008 R2.