By referring to the network structure and OSPF areas shown in the figure, it can...

Comprehensive Explanation: In OSPF, an Area Border Router (ABR) is a router that has interfaces in more than one OSPF area, facilitating communication between different areas. If a router has interfaces in only one OSPF area, it is not an ABR. Based on the network structure, it is incorrect to assume that all routers except RTA are ABRs. A router can only be considered an ABR if it has interfaces connecting to multiple OSPF areas. If a router only connects within one area, it is not an ABR.