Your network contains an Active Directory forest. The forest contains one domain named
contoso.com.
You attempt to run adprep /domainprep and the operation fails.
You discover that the first domain controller deployed to the forest failed.
You need to run adprep /domainprep successfully.
What should you do?

A.
Move the domain naming master role.

B.
Install a read-only domain controller (RODC).

C.
Move the PDC emulator role.

D.
Move the RID master role.

E.
Move the infrastructure master role.

F.
Deploy an additional global catalog server.

G.
Move the bridgehead server.

H.
Move the schema master role.

I.
Restart the Active Directory Domain Services (AD DS) service.

J.
Move the global catalog server.

Explanation:
Adprep /domainprep must be run on the server holding the Infrastructure Master role. The
role was originally installed on the first domain controller in the forest. Now it’s down and
another domain controller must get the Infrastructure Master role.

Reference 1)
http://technet.microsoft.com/en-us/library/cc754889.aspx
Planning Operations Master Role Placement
Operations master role holders are assigned automatically when the first domain controller
in a given domain is created. The two forest-level roles (schema master and domain naming
master) are assigned to the first domain controller created in a forest. In addition, the three
domain-level roles (RID master, infrastructure master, and PDC emulator) are assigned to
the first domain controller created in a domain.
Reference 2)
http://technet.microsoft.com/en-us/library/dd464018.aspx
Adprep /domainprep Must be run on the infrastructure operations master for the domain.