You need to ensure that all of the Exchange Server services in Branch1 are available if the WAN link fails after the planned deployment

Your network contains an Active Directory forest. The forest contains one domain. The domain
contains two sites and three domain controllers. The sites and domain controllers are configured as
shown in the following table.

The sites connect to each other by using a WAN link. You have an Exchange Server 2013 organization
that contains two servers in the Main Office site. In Branch1, you plan to deploy one server to the
Exchange Server 2013 organization. You need to ensure that all of the Exchange Server services in
Branch1 are available if the WAN link fails after the planned deployment. What should you do?

A.
Create a site link bridge, and then configure Branch1 as a hub site.

B.
Replace the domain controller in Branch1 with an RODC that runs Windows Server 2012.

C.
Replace the domain controller in Branch1 with a writable domain controller that runs a Server
Core installation of Windows Server 2008.

D.
Create an additional site link, and then configure Branch1 as a hub site.

Explanation:
Site link bridge
A site link bridge connects two or more site links and enables transitivity between site links. Each site
link in a bridge must have a site in common with another site link in the bridge. The Knowledge
Consistency Checker (KCC) uses the information on each site link to compute the cost of replication
between sites in one site link and sites in the other site links of the bridge. Without the presence of a
common site between site links, the KCC also cannot establish direct connections between domain
controllers in the sites that are connected by the same site link bridge. By default, all site links are transitive.

This figure illustrates an organization’s hub-and-spoke network topology, consisting of two hub sites
(A and B) and six satellite sites (C through H). The site links between all sites are named A-B, A-C, AD, A-E, B-F, B-G, and B-H.

Hub Site
A hub site is based on having large numbers of outgoing links
NOT A B D
If you want to install or operate any Exchange 2013 server in a site, you must have a writable global
catalog in the same AD site.
Be aware that no versions of Exchange Server will make use of RODC or the Global Catalog server on
a RODC although Exchange will work in the presence of RODC as long as writable versions of domain
controllers and GCs are available
C
If you want to install or operate any Exchange 2013 server in a site, you must have a writable global
catalog in the same AD site.

The Global Catalog is the central repository of information about objects in a tree or forest but with
a limited number of each objects attribute.
The domain controller that holds a copy of the Global Catalog is the Global Catalog Server.
The global catalog server makes it possible to search the entire AD DS forest without referrals to the
domain controller that stores the target of the search.
The global catalog server is also required for searching and processing domain logons in forests
where universal groups is available Be aware that no versions of Exchange Server will make use of
RODC or the Global Catalog server on a RODC although Exchange will work in the presence of RODC
as long as writable versions of domain controllers and GCs are available