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.