You need to compact an Active Directory database ona domain controller that runs Windows Server 2008 R2.
What should you do?

A.
Run defrag.exe /a /c.

B.
Run defrag.exe /c /u.

C.
From Ntdsutil, use the Files option.

D.
From Ntdsutil, use the Metadata cleanup option.

Explanation:
Reference 1:
http://technet.microsoft.com/en-us/library/cc794920.aspx
Compact the Directory Database File (Offline Defragmentation)
You can use this procedure to compactthe Active Directory database offline. Offline defragmentation returns
free disk space in the Active Directory database tothe file system. As part of the offline defragmentation
procedure, check directory database integrity.
Performing offline defragmentation creates a new, compacted version of the database filein a different
location.
Reference 2:
Mastering Windows Server 2008 R2 (Sybex, 2010)
page 805
Performing Offline Defragmentation of Ntds.dit
These steps assume that you will be compacting the Ntds.dit file to a local folder. If you plan to defragment and
compact the database to a remote shared folder, mapa drive letter to that shared folder before you begin these
steps, and use that drive letter in the path where appropriate.
1. Open an elevated command prompt. Click Start, andthen right-click Command Prompt. Click Run as
Administrator.
2. Type ntdsutil, and then press Enter.
3. Type Activate instance NTDS, and press Enter.
4. At the resulting ntdsutil prompt, type Files(case sensitive), and then press Enter.
5. At the file maintenance prompt, type compact tofollowed by the path to the destination folder forthe
defragmentation, and then press Enter.