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 data file of the undo tablespace is autoextensible

B.
When there are more than one undo tablespace 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