Which traffic should you permit through the firewall?

Your network consists of one Active Directory domain.
The network contains one Active Directory site.
All domain controllers run Windows Server 2008.
You create a second Active Directory site and plan to install a domain controller that runs Windows Server 2008 in the new site.
You also plan to deploy a new firewall to connect the two sites.

You need to enable the domain controllers to replicate between the two sites.

Which traffic should you permit through the firewall?

A.
LDAP

B.
NetBIOS

C.
RPC

D.
SMTP