Your network contains several branch offices. All servers run Windows Server 2008 R2. Each branch office contains a domain controller and a file server. The DHCP Server server role is installed on the branch office domain controllers. Each office has a branch office administrator. You need to delegate the administration of DHCP to meet the following requirements： èAllow branch office administrators to manage DHCP scopes for their own office èPrevent the branch office administrators from managing DHCP scopes in other offices èMinimize administrative effort. What should you do？（）

A. In the Active Directory domain， add the branch office administrators to the Server Operators built-in local group.
B. In the Active Directory domain，add the branch office administrators to the NetworkConfiguration Operators built-in local group.
C. In each branch office， migrate the DHCP Server server role to the file server. On each fileserver， add the branch office administrator to the DHCP Administrators local group.
D. n each branch office， migrate the DHCP Server server role to the file server. In the Active Directory domain， add the branch office administrators to the DHCP Administrators domain local group.