Your company has a main office and a branch office. You deploy a read-only domain
controller (RODC) that runs Microsoft Windows Server 2008 to the branch office.
You need to ensure that users at the branch office are able to log on to the domain by using
the RODC.
What should you do?

A.
Add another RODC to the branch office.

B.
Configure a new bridgehead server in the main office.

C.
Decrease the replication interval for all connection objects by using the Active Directory
Sites and Services console.

D.
Configure the Password Replication Policy on the RODC.

Explanation:
Answer) Configure the Password Replication Policy on the RODC.

http://technet.microsoft.com/en-us/library/cc754956%28v=ws.10%29.aspx
RODC Frequently Asked Questions
What new attributes support the RODC Password Replication Policy?
Password Replication Policy is the mechanism for determining whether a user or computer’s
credentials are allowed to replicate from a writable domain controller to an RODC. The
Password Replication Policy is always set on a writable domain controller running Windows
Server 2008.
What operations fail if the WAN is offline, but the RODC is online in the branch office?
If the RODC cannot connect to a writable domain controller running Windows Server 2008 in
the hub, the following branch office operations fail:
Password changes
Attempts to join a computer to a domain
Computer rename
Authentication attempts for accounts whose credentials are not cached on the RODC
Group Policy updates that an administrator might attempt by running the gpupdate /force
command
What operations succeed if the WAN is offline, but the RODC is online in the branch office?
If the RODC cannot connect to a writable domain controller running Windows Server 2008 in
the hub, the following branch office operations succeed:
Authentication and logon attempts, if the credentials for the resource and the requester are
already cached, Local RODC server administration performed by a delegated RODC server
administrator.