Refer to the exhibit.
Which two topology changes happen to the IS-IS routers? (Choose two.)
A. All four routers are operating as Level 1 routers only.
B. All four routers are operating as Level 2 routers only.
C. R1 and R4 are Level 2 neighbours.
D. R1 and R2 are Level 2 neighbours.
E. All four routers are operating as Level 1-2 routers.