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

Which two statements about IS-IS are correct? (Choose two.)
A . Level 1 intermediate systems exchange routing information with Level 1 intermediate systems in other IS-IS areas.
B . An IS-IS router sets the attached bit in the PDUs it sends to a Level 1 area to indicate that it is a backbone router.
C . A Level 1 router can only form adjacencies with other Level 1 routers.
D . Level 2 routers can form adjacencies with either Level 1 or Level 2 routers.

Answer: B,C