Several remote sales employees， who have come into the office this week， report that they are unable to get on the Internet， but no other users have reported similar issues.  The help desk hasescalated the issue and the case notes state that the users have IP addresses that begin with 169. Which of the following should the system administrator check FIRST？（）

• A、DHCP server
• B、Network switches
• C、DNS server
• D、Core router