A loopback plug is a diagnostic tool used to test the functionality of network interfaces by creating a signal loop. In this case, since the user's device is hardwired to the network but cannot access the internet, using a loopback plug can help determine whether the issue is with the network interface card (NIC) or the Ethernet cable. * A. Loopback plug: This tool helps test whether the computer's network interface is functioning properly. Why the other options are incorrect: * B. Network tap: A network tap is used to monitor network traffic, but it wouldn't help diagnose the local connectivity issue here. * C. Wi-Fi analyzer: This tool is used to troubleshoot Wi-Fi networks, but since the issue is with a hardwired connection, it's not applicable. * D. Punchdown tool: A punchdown tool is used to connect network cables to a patch panel or keystone jack. It is not used for diagnosing network issues. This falls under the Hardware and Network Troubleshooting domain in the CompTIA A+ Core 1 exam.