A System Administrator Reports That One of the Two Domain

A system administrator reports that one of the two domain name servers does not seem to be responding to DNS requests from clients. The servers are both up and running, name service is running on them, and DNS requests appear in the logs. Both servers respond to queries made at the console. Which of the following tools should the systems administrator use to gather more information?

A) Run a port scanner on each name server to ensure TCP port 53 is open and listening.
B) Run tracert from a desktop client to query each name server and see what answers are sent back from each server. Run tracert from a desktop client to query each name server and see what answers are sent back from each server.
C) Ping the name servers by IP address to make sure they are up, and then ping each name server by name in case name resolution is not working for the server names.
D) Generate DNS queries and use a packet sniffer to capture DNS traffic to/from both name servers and look for differences.