Which three statements about BGP confederation and route reflectors are true？ （）
- AClusters are used in confederation schemes to avoid loops.
- BBGP network can have a confederation within a route reflector area.
- CAn internal BGP network cannot have a route reflector within a confederation.
- DAn internal BGP network can have a route reflector within a confederation.
- EClusters are used in route reflector schemes to avoid loops.
- FBGP network cannot have a confederation within a route reflector area.