Which two statements are true by default of a multilevel IS-IS network?（）

• A、Level 1 only routers see routes contained in their area.
• B、Level 1 routers route towards Level 2 routers due to the attached bit.
• C、Level 2 routers route towards Level 1 routers due to the attached bit.
• D、Level 2 routers can see routes in other Level 2 areas and routes originated in Level 1 areas.