You are the network administrator for .Your network consists of a single Active Directory domain named . The Default Domain Group Policy object (GPO) uses all default settings. The network contains five servers running Windows Server 2003 and 800 client computers. Half of the client computers are portable computers. The other half are desktop computers. Users of portable computers often work offline, but users of desktop computers do not. You install Windows XP Professional on all client computers with default settings. Then you configure user profiles and store them on the network. Some users of portable computers now report that they cannot log on to their computers. Other users of portable computers do not experience this problem. You need to ensure that all users of portable computers can log on successfully,whether they are working online or offline. What should you do?（）

• A、Configure all portable computers to cache user credentials locally.
• B、Ensure that all users of portable computers log on to the network at least once before working offline.
• C、In all portable computers, rename Ntuser.dat to Ntuser.man.
• D、For all portable computers, configure the Loopback policy setting.