Which two statements are true about IS-IS? (Choose two.)

A.
All level 2 PDUs are flooded to Level 1 by default.

B.
All level 1 PDUs are flooded to Level 2 by default.

C.
Both Level 1 and Level 2 adjacencies can exist on the same interface.

D.
Level 2 external routes are always available in Level 1.