The answer is C. Test the theory to determine the cause.
According to the CompTIA A+ troubleshooting methodology, the steps to troubleshoot any problem are:
* Identify the problem and act
* Establish a theory of probable cause
* Test the theory to determine the cause
* Establish a plan of action to resolve the problem and implement the solution
* Verify system functionality and implement preventive measures
* Document key findings, actions, and outcomes
In this scenario, the technician has already identified the problem (trouble accessing files on the network) and established a theory of probable cause (a failed NIC). The next step is to test the theory to determine the cause, which involves verifying whether the NIC is working properly or not.
Some possible ways to test the theory are:
* Check the physical connection and status of the NIC port and cable12
* Check the link state and speed of the NIC using ethtool or ip commands2
* Check the configuration and state of the NIC using nmcli, teamdctl, or teamnl commands2
* Check the driver and firmware of the NIC using lspci, modinfo, or dmesg commands2
* Check the logs for any errors or warnings related to the NIC using journalctl or grep commands2
* Uninstall and reinstall the NIC driver using Device Manager or modprobe commands13
* Replace the NIC or cable with a known good one and test again13
If any of these tests confirm that the NIC is faulty, then the technician can proceed with the next step of establishing a plan of action to resolve the problem and implement the solution. If none of these tests reveal any issues with the NIC, then the technician can eliminate it as a probable cause and look for other possible causes. Therefore, option C is the correct answer.