The best action to take when a specific subnet cannot be reached from various hosts is to verify that the subnet is correctly listed in the router's routing table. If the missing route to the target subnet is not in the routing table, traffic directed to that subnet will not be delivered because routers rely on these tables to make forwarding decisions. Adding the correct route to the table will solve the connectivity issue, assuming there are no other underlying problems. The other options, although plausible, do not directly address the issue of the missing route. Checking cables is unrelated to routing table configurations; reconfiguring network settings on all hosts is inefficient and does not target the suspected issue; enabling a routing protocol might be a necessary step but only if the route cannot be statically entered or is dynamically changing.