To make OSPF area 4 totally stubby, the following command was issued on the ABR in router configuration mode: area 4 stub.Which two things need to be done to finish making area 4 a totally stubby area?（）
A. Apply the area 4 stub command to all routers in the area
B. On the ABR, use the area 4 stub command with the no - summary keyword
C. On the ABR, specify a default cost for the area with the area default - cost command
D. On the ABR, use the default - information originate command to inject a default route into area 4
E. Use the auto - cost command on each router in the area to automatically determine the cost to other OSPF areas
正确答案：参考A, B
