You work as the enterprise exchange administrator at TestKing.com. TestKing.com makes use of
Microsoft Exchange Server messaging solution. TestKing.com has its headquarters in Chicago and branchoffices around the globe. All the offices of Testking.com have a direct link to the Internet.
The Chicago office connects to the other offices via a WAN link. You have received instructions from theCIO to install Exchange Server 2010 servers in every office. You need to ensure that your design maintainuser access mailboxes in the event of a domain controller failure as well as ensuring that user is able tosend e-mail messages if a WAN link failure should occur.
What should you do？（）

A.Your best option should be create an Active Directory site for every office.Thereafter one domain controller and two read only domain controllers should be deployed in everysite.
B.Your best option should be create an Active Directory site for every office.Thereafter two domain controllers should be deployed for every site.
C.Your best option should be create an Active Directory site for every office.Thereafter a single domain controller should be deployed in every site and site link bridging enabled.
D.Your best option should be create an Active Directory site for every office.Thereafter a single domain controller and a read only domain controller should be deployed in everysite.