Your database contains at least one undo tablespace. You attempt to start an instance in Automatic Undo Management mode, but without specifying an undo tablespace in the initialization parameter file. What happens?
The instance will not start.
The instance starts up and uses the SYSTEM rollback segment for all undo entries.
The instance starts up and uses the SYSTEM tablespace for the automatic undo segments.
The instance starts up and uses the first available undo tablespace for the automatic undo segments.