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

Which two statements are true about IS-IS levels? (Choose two.)
A . Level 2 systems do not advertise Level 2 routes into a Level area by default.
B . Level 2 systems must use the loopback address as a part of the ISO network address.
C . Level 1 system only from adjacencies with other systems that have different area IDs.
D . Level 1 systems use a default route to reach AS external routes located in other areas.

Answer: A,D