Your company has a main office and a branch office. Your network consists of a single Active Directory domain. All domain controllers are in the main office. The offices connect to one another by using a wide area network (WAN) link. The branch office has a computer named Server1 that runs Windows Server 2003 Service Pack 2 (SP2). A domain user named User1 reports that he cannot log on to Server1 when the WAN link is unavailable. He reports that he can log on to Server1 when the WAN link is available. You need to ensure that User1 can log on to Server1 by using his domain account when the WAN link is unavailable. What should you do?（）

A. Modify the Default Domain Policy.
B. Modify the Default Domain Controller Policy.
C. Add User1 to the Domain Admins group in the domain.
D. Add User1 to the local Administrators group on Server1.