Which two statements are true by default of a multilevel IS-IS network?()
A、A. Level 1 only routers see routes contained in their area.
B、B. Level 1 routers route towards Level 2 routers due to the attached bit.
C、C. Level 2 routers route towards Level 1 routers due to the attached bit.
D、D. Level 2 routers can see routes in other Level 2 areas and routes originated in Level 1 areas.