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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.

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出自：Oracle认证

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