When is the UNDO_RETENTION parameter value ignored by a transaction?

When is the UNDO_RETENTION parameter value ignored by a transaction?

A.
when Flashback Database is enabled

B.
when the data file of the undo tablespace is autoextensible

C.
when there are multiple undotablespaces available in a database

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