A. 172.16.1.0/25 because it is the first ultimate route
B. 0.0.0.0/0 because it is the lowest network number
C. 172.16.0.0/25 because it is the first level 1 route
D. 172.18.0.0/15 because it has the shortest mask
B. 0.0.0.0/0 because it is the lowest network number
C. 172.16.0.0/25 because it is the first level 1 route
D. 172.18.0.0/15 because it has the shortest mask