Your network contains an Active Directory domain. All domain controllers run Windows Server 2008  R2. Client computers run either Windows XP Service Pack 3 （SP3） or Windows Vista.  You need to ensure that all client computers can apply Group Policy preferences.   What should you do（）

• A、Upgrade all Windows XP client computers to Windows 7.
• B、Create a central store that contains the Group Policy ADMX files.
• C、Install the Group Policy client-side extensions （CSEs） on all client computers.
• D、Upgrade all Windows Vista client computers to Windows Vista Service Pack 2 （SP2）.