Explanation
Our new static default route has the Administrative Distance (AD) of 120, which is bigger than the AD of OSPF External route (O*E2) so it will not be pushed into the routing table until the current OSPF External route is removed.For your information, if you don't type the AD of 120 (using the command "ip route 0.0.0.0
0.0.0.0 10.13.0.1") then the new static default route would replace the OSPF default route as the default AD of static route is 1. You will see such line in the routing table:S* 0.0.0.0/0 [1/0] via 10.13.0.1

Since all the same router (C-router) is the default gateway for all three VLANs, all traffic destined to a different VLAN will be sent to the C-router. The C-router will have knowledge of all three networks since they will appear as directly connected in the routing table. Since the C-router already knows how to get to all three networks, no routing protocols need to be configured.