A Wi-Fi router is set up in a central room.

CompTIA A+ explains that Wi-Fi issues at the edges of a building are typically caused by weak signal coverage, not client configuration. The recommended solution is to add additional wireless access points (APs) or mesh extenders to expand coverage and eliminate dead zones.

Enabling 5GHz would worsen the problem because 5GHz has shorter range and penetrates walls less effectively than 2.4GHz. Flushing DNS affects name resolution, not wireless signal strength. Upgrading the NIC to Wi-Fi 6 improves maximum throughput but still depends on sufficient signal, which the user does not have.

Additional APs ensure strong signal-to-noise ratio, consistent throughput, and stable roaming all solutions emphasized in the A+ wireless troubleshooting section. Therefore, option D is the correct and CompTIA-aligned fix.