In which situation may the UNDO_RETENTION parameter be ignored， even if it is set to a value（）

• A、when the data file of the undo tablespace is autoextensible
• B、when there are more than one undo tablespaces available in the database
• C、when the undo tablespace is of a fixed size and retention guarantee is not enabled
• D、when the undo tablespace is autoextensible and retention guarantee is not enabled