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You want to make use of the object features available in the database for the form module you are developing. Which three statements about object types are true? （）
A:An object type is a user-defined composite data type. 
B:The attributes of an object type can be those of other object types. 
C:A PL/SQL table of records is an example of a nested object type. 
D:An object type must be declared as a type before the actual object itself can be declared.

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出自：Oracle认证

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