In the topology shown in the figure, the following configurations are performed on RTA, RTB, RTC, and RTD respectively:
RTA-LoopBack0] ip address 1.1.1.1 255.255.255.255
RTA]ospf 1
RTA-ospf-1]area 1
RTA-ospf-1-area-0.0.0.1]network 10.0.0.0 0.0.0.255
RTA-ospf-1]import-route direct
RTB-LoopBack0] ip address 2.2.2.2 255.255.255.255
RTB]ospf 1
RTB-ospf-1]area 1
RTB-ospf-1-area-0.0.0.1]network 10.0.0.0 0.0.0.255
RTB-ospf-1-area-0.0.0.1]area 0
RTB-ospf-1-area-0.0.0.0]network 2.2.2.2 0.0.0.0
RTB-ospf-1-area-0.0.0.0]network 20.0.0.0 0.0.0.255
RTC-LoopBack0] ip address 3.3.3.3 255.255.255.255
RTC]ospf 1
RTC-ospf-1]area 0
RTC-ospf-1-area-0.0.0.0]network 20.0.0.0 0.0.0.255
RTC-ospf-1-area-0.0.0.0]area 2
RTC-ospf-1-area-0.0.0.2]nssa no-import-route no-summarRTC-ospf-1-area-0.0.0.2]network 30.0.0.0
0.0.0.255
RTC-ospf-1]import-route direct
RTD-LoopBack0] ip address 4.4.4.4 255.255.255.255
RTD]ospf 1
RTD-ospf-1]area 2
RTD-ospf-1-area-0.0.0.2]network 30.0.0.0 0.0.0.255
RTD-ospf-1-area-0.0.0.2]network 4.4.4.4 0.0.0.0
RTD-ospf-1-area-0.0.0.2]nssa
Then _______ may be injected into the backbone area

RTA and RTB run the BGP routing protocol, and there is a static default route on RTA at the same time.
The correct way to import the default route in RTA into BGP is ______

In the OSI network system, what has the similar function as the IP protocol in TCP/IP is _________.

Which of the following descriptions about Route-polic is correct is ______?

In the OSPF protocol, the types of LSAs that ASBRs cannot aggregate are _______