Your network contains an Active Directory domain. The domain contains three domain
controllers.
One of the domain controllers fails.
Seven days later, the help desk reports that it can no longer create user accounts. You need
to ensure that the help desk can create new user accounts.
Which operations master role should you seize?

A.
domain naming master

B.
infrastructure master

C.
primary domain controller (PDC) emulator

D.
RID master

E.
schema master

Explanation:
http://technet.microsoft.com/en-us/library/cc773108%28v=ws.10%29.aspx
Operations master roles

Active Directory supports multimaster replication of the directory data store between all
domain controllers (DC) in the domain, so all domain controllers in a domain are essentially
peers. However, some changes are impractical to perform in using multimaster replication,
so, for each of these types of changes, one domain controller, called the operations master,
accepts requests for such changes.
In every forest, there are at least five operations master roles that are assigned to one or
more domain controllers. Forest-wide operations master roles must appear only once in
every forest. Domain-wide operations master roles must appear once in every domain in the
forest.
..
RID master
The RID master allocates sequences of relative IDs (RIDs) to each of the various domain
controllers in its domain. At any time, there can be only one domain controller acting as the
RID master in each domain in the forest.
Whenever a domain controller creates a user, group, or computer object, it assigns the
object a unique security ID (SID). The SID consists of a domain SID, which is the same for
all SIDs created in the domain, and a RID, which is unique for each SID created in the
domain.
To move an object between domains (using Movetree.exe), you must initiate the move on
the domain controller acting as the RID master of the domain that currently contains the
object.
http://www.techrepublic.com/article/step-by-step-learn-how-to-transfer-and-seize-fsmo-rolesin-activedirectory/
5081138
Step-By-Step: Learn how to transfer and seize FSMO roles in Active Directory
http://www.petri.co.il/seizing_fsmo_roles.htm
Seizing FSMO Roles