[单项选择]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