Your companys Windows Server 2003 environment consists of a single Active Directory directory service forest. The forest has multiple domains and three sites named Site1， Site2， and Site3. Site1 is the main office and has four domain controllers. Two of the domain controllers are global catalog servers. Site2 is a branch office with two domain controllers. Site3 is a branch office with a slow and unreliable WAN link and two domain controllers.  You need to improve user logon performance for users in Site2 and Site3.  Which two actions should you perform？（）

• A、 Enable change notification between Site1 and Site2.
• B、 Enable change notification between Site1 and Site3.
• C、 Implement universal group membership caching in Site2.
• D、 Implement universal group membership caching in Site3.