The following statements about the ISIS protocol route aggregation, which are correct?

The following statements about the ISIS protocol route aggregation, which are correct?
A . Route aggregation can be configured and validated on all types of routers.
B . Route aggregation can only be configured on the level-1 router to take effect.
C . Route aggregation can only be configured on the level-2 router to take effect.
D . Route aggregation can only be configured on the level-1-2 router to take effect.

Answer: A