Your company has an Active Directory domain.
You log on to the domain controller. The Active Directory Schema snap-in is not available in
the Microsoft Management Console (MMC).
You need to access the Active Directory Schema snap-in.
What should you do?

A.
Add the Active Directory Lightweight Directory Services (AD LDS) role to the domain
controller by using Server Manager.

B.
Log off and log on again by using an account that is a member of the Schema
Administrators group.

C.
Use the Ntdsutil.exe command to connect to the Schema Master operations master and
open the schema for writing.

D.
Register Schmmgmt.dll.

Explanation:
http://technet.microsoft.com/en-us/library/cc732110.aspx
Install the Active Directory Schema Snap-In

You can use this procedure to first register the dynamic-link library (DLL) that is required for
the Active Directory Schema snap-in. You can then add the snap-in to Microsoft
Management Console (MMC).
To install the Active Directory Schema snap-in
1. To open an elevated command prompt, click Start, type command prompt and then rightclick Command
Prompt when it appears in the Start menu. Next, click Run as administrator and then click
OK.
To open an elevated command prompt in Windows Server 2012, click Start, type cmd, right
click cmd and then click Run as administrator.
2. Type the following command, and then press ENTER:
regsvr32 schmmgmt.dll
3. Click Start, click Run, type mmc and then click OK.
4. On the File menu, click Add/Remove Snap-in.
5. Under Available snap-ins, click Active Directory Schema, click Add and then click OK.
6. To save this console, on the File menu, click Save.
7. In the Save As dialog box, do one of the following:
* To place the snap-in in the Administrative Tools folder, in File name, type a name for the
snap-in, and then click Save.
* To save the snap-in to a location other than the Administrative Tools folder, in Save in
navigate to a location for the snap-in. In File name, type a name for the snap-in, and then
click Save