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.

Explanation:
Note: For IS-IS, you cannot apply routing policies that affect how routes are imported into the routing table; doing so with a link-state protocol can easily lead to an inconsistent topology database.

You can administratively divide a single AS into smaller groups called areas. You configure each router interface to be in an area. Any interface can be in any area. The area address applies to the entire router; you cannot specify one interface to be in one area and another interface in a different area. In order to route between areas you must have two adjacent Level2 routers that communicate with each other.
Level1 routers can only route within their IS-IS area. To send traffic outside their area, Level1 routers must send packets to the nearest intra-area Level2 router. A router can be a Level1 router, a Level2 router, or both. You specify the router level on a per-interface basis, and a router becomes adjacent with other routers on the same level on that link only.

You can configure one Level1 routing process and one Level2 routing process on each interface, and you can configure the two levels differently.