问题：

[单选] You need to design an administrative model for the Exchange Server environment. What should you do？（）

A . Create a single organizational unit （OU）. Place the user accounts for each office in the OU. Delegate control over the OU to the office’s server administrators and the central IT staff
B . Create a single Exchange administrative group. Place all Exchange servers into that administrative group. Assign permissions for the administrative group to the officer’s server administrators and the central IT staff
C . Create an Exchange administrative group for each office. Place the Exchange severs for each office into that office’s administrative group. Assign permissions for the administrative group to the office’s server administrators. Allow the central IT staff to manage user mailboxes
D . Create an organizational unit （OU） for each office. Place the user accounts for each office into the appropriate OU. Delegate control over each OU to the office’s server administrators. Allow the central IT staff to manager user mailboxe