You are the network administrator for Blue Yonder Airlines. You plan to create an Active Directory domain named blueyonderairlines.com that will have a functional level of Windows Server 2003.  Your company has one main office and four branch offices， which are all located in one country. A central security department in the main office is responsible for creating and administering all user accounts in all offices. Each office has a local help desk department that is responsible for resetting passwordswithin the individual department’s office only.  All user accounts are located in the default Users container.  You need to create an organizational unit （OU） structure to support the delegation of authority requirements. You want to minimize the amount of administrative effort required to maintain the environment.  What should you do？（）