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 the domain 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, see the reference below.

Windows Server 2008 R2 Unleashed (SAMS, 2010) pages 1292 and 1297
Active Directory Recycle Bin Recovery
Let’s 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.