Your network contains an Active Directory forest named contoso.com. The functional level of
the forest is Windows Server 2008 R2. The forest contains a single domain.
You need to ensure that objects can be restored from the Active Directory Recycle Bin.
Which tool should you use?

A.
Ntdsutil

B.
Set-ADDomain

C.
Dsamain

D.
Enable-ADOptionalFeature

Explanation:
Similar question to question E/Q28

http://technet.microsoft.com/en-us/library/dd379481.aspx
Enabling Active Directory Recycle Bin
After the forest functional level of your environment is set to Windows Server 2008 R2, you
can enable Active Directory Recycle Bin by using the following methods:

Enable-ADOptionalFeature Active Directory module cmdlet (This is the recommended
method.)
Ldp.exe