In the topology shown in the figure, the following configurations are performed on RTA, RTB, RTC and RTD respectively:
RTA] ospf 1 router-id 1.1.1.1
RTA-ospf-1] area 0
RTA-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
RTA-ospf-1-area-0.0.0.0] network 1.1.1.1 0.0.0.0
RTB] ospf 1 router-id 2.2.2.2
RTB-ospf-1] area 0
RTB-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255
RTB-ospf-1-area-0.0.0.0] network 2.2.2.2 0.0.0.0
RTB-ospf-1] area 1
RTB-ospf-1-area-0.0.0.1] network 192.168.2.0 0.0.0.255
RTB-ospf-1-area-0.0.0.1] vlink-peer 3.3.3.3
RTC] ospf 1 router-id 3.3.3.3
RTC] ospf 1]import direct
RTC-ospf-1] area 1
RTC-ospf-1-area-0.0.0.1] network 192.168.2.0 0.0.0.255
RTC-ospf-1-area-0.0.0.1] vlink-peer 2.2.2.2
RTC-ospf-1] area 2
RTC-ospf-1-area-0.0.0.2] network 192.168.3.0 0.0.0.255
RTD] ospf 1 router-id 4.4.4.4
RTD-ospf-1] area 2
RTD-ospf-1-area-0.0.0.2] network 192.168.3.0 0.0.0.255
RTD-ospf-1-area-0.0.0.2] network 4.4.4.4 0.0.0.0
Then the router type in the OSPF area of RTC is _______

B As shown in the figure, RTA, RTB, and RTC run OSPF, and the process number is 100; OSPF process 200 runs between RTA, RTB, and RTD. The cost of all interconnected links is set to 10. Set the external route priority of OSPF 100 on RTA and RTB to 190, and import an external route 172.16.1.0/24 into OSPF 100 on RTC. Both RTA and RTB are configured to import OSPF100 routes into OSPF200.
According to the above scenario analysis, the following description about RTD learning external routing 172.16.1.0/24 is correct.

In the IS-IS network as shown in the figure, RTA, RTC, RTD, and RTE establish a Level-2 adjacency relationship with each other; RTB, RTA, and RTC establish a Level-1 adjacency relationship. After the reason of each router is stable, when RTB accesses 192.168.5.1, it chooses the next hop as ______.
If RTA adds the following configuration at this time:
RTA-isis-1]import-route isis level-2 into level-1
Then when RTB accesses 192.168.5.1 again, choose the next hop as ______.

After the BGP router receives the route from the peer, its basic operation is _________.

In the IS-IS network as shown in the figure, after the routes of each router are stable, there are ______ IS-IS Level-1 routes learned by RTC through neighbors.