You are a network administrator for your company. All domain controllers run Windows Server 2003. The network contains 50 Windows 98 client computers， 300 Windows 2000 Professional computers， and 150 Windows XP Professional computers.   According to the network design specification， the Kerberos version 5 authentication protocol must be used for all client computers on the internal network.   You need to ensure that Kerberos version 5 authentication is used for all client computers on the internal network.  What should you do？ （）

• A、 On each domain controller, disable Server Message Block (SMB) signing and encryption of the secure channel traffic.  
• B、 Replace all Windows 98 computers with new Windows XP Professional computers.  
• C、 Install the Active Directory Client Extensions software on the Windows 98 computers. 
• D、 Upgrade all Windows 98 computers to Windows NT Workstation 4.0.