Correct Answer. A. That the router has the correct subnet masks configured for each interface Incorrect subnet masks can prevent routing between interfaces on a router, leading to connectivity issues between subnets.
Option B is incorrect. While DHCP is important for IP address assignment, it does not directly resolve routing issues between subnets.
Option C is incorrect. The category of network cables would impact physical connectivity and data rates but not routing between subnets.
Option D is incorrect. While firewall settings are crucial, the first check should be the configuration that directly impacts routing.