Which configuration should you use?

Your network contains an Active Directory domain named contoso.com.
The domain contains a main office and a branch office.
An Active Directory site exists for each office.
The domain contains two servers named SERVER1 and SERVER2 that run Windows Server 2012.
Both servers have the DHCP Server server role installed. SERVER1 is located in the main office site.
SERVER2 is located in the branch office site. SERVER1 provides IPv4 addresses to the client computers in the
main office site.
SERVER2 provides IPv4 addresses to the client computers in the branch office site.
You need to ensure that if either SERVER1 or SERVER2 are offline, the client computers can still obtain IPv4
addresses.
The solution must meet the following requirements:
The storage location of the DHCP databases must not be a single point of failure.
SERVER1 must provide IPv4 addresses to the clientcomputers in the branch office site only if SERVER2 is
offline.
SERVER2 must provide IPv4 addresses to the clientcomputers in the main office site only if SERVER1 is
offline.
Which configuration should you use?

A.
Load sharing mode failover partners

B.
Hot standby mode failover partners

C.
A Network Load Balancing (NLB) cluster

D.
A failover cluster

Explanation:
http://technet.microsoft.com/en-us/library/hh831385.aspx