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