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

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

A.
When the undo tablespace is autoextensible and retention guarantee is not enabled

B.
When there are more than one undo tablespace available in the database

C.
When the data file of the undo tablespace is autoextensible

D.
When the undo tablespace is of a fixed size and retention guarantee is not enabled