[单项选择]In which situation is 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