Which three statements are true about the Oracle Data Dictionary? (Choose three.)

A: Data dictionary views are created by joins of dictionary base tables and DBA-defined tables B: The data dictionary is created and maintained by the database administrator C: Views with the same name but different prefixes, such as CDB, DBA, ALL and USER, reference the same base tables from the data dictionary D: Base tables can be queried directly E: It is owned by the SYSTEM user F: Usernames of all users including database administrators are stored in the data dictionary