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.