Your network contains an Active Directory forest. The forest contains domain controllers that run Windows
Server 2008 R2. The functional level of the forest is Windows Server 2003. The functional level of thedomain is
Windows Server 2008.
From a domain controller, you need to perform an authoritative restore of an organizational unit (OU).
What should you do first?

A.
Raise the functional level of the forest

B.
Modify the tombstone lifetime of the forest.

C.
Restore the system state.

D.
Raise the functional level of the domain.

Explanation:
The Recycle Bin feature cannot be applied here, seethe reference below.
Reference:
Windows Server 2008 R2 Unleashed (SAMS, 2010)
pages 1292 and 1297
Active Directory Recycle Bin Recovery
Lets begin this section with a very clear statement: If you need to recover a deleted Active Directory object and
the Active Directory Recycle Bin was not enabled before the object was deleted, skip this section and proceed
to the Active Directory Authoritative Restore section.
Active Directory Authoritative Restore
When Active Directory has been modified and needs to be restored to a previous state, and this rollback needs
to be replicated to all domain controllers in the domain and possibly the forest, an authoritative restore of Active
Directory is required. An authoritative restore of Active Directory can include the entire Active Directory
database, a single object, or a container, such as an organizational unit including all objects previously stored
within the container. To perform an authoritative restore of Active Directory, perform the System State
restore of a domain controller.