A network technician receives a ticket that all users can no longer access an Intranet web application. The network monitoring tool shows that the server hosting the web application responds to ICMP echo requests and DNS resolves. Which of the following is the FIRST question the network technician should ask the server administrator?

A.
Have any changes been implemented on the server?

B.
Is there a backup server available?

C.
Is the application listening port active?

D.
How many connections are currently established?