Which statement describes IS-IS operation?

Which statement describes IS-IS operation?

A.
Routes in a Level 2 area are advertised into Level 1 areas by default.

B.
To advertise Level 2 routes into a Level 1 area, an export policy must be configured.

C.
Level 1 routes are not advertised into Level 2 by default.

D.
The Level 2 router advertises a default route into Level 1.