Which four statements are true?()
A、Has-a relationships should never be encapsulated.
B、Has-a relationships should be implemented using inheritance.
C、Has-a relationships can be implemented using instance variables.
D、Is-a relationships can be implemented using the extends keyword.
E、Is-a relationships can be implemented using the implements keyword.
F、An array or a collection can be used to implement a one-to-many has-a relationship.