You have a production instance running on your server. UNDO_RETENTION is not long enough to satisfy read-consistency requirements.
How do you change the UNDO_RETENTION value?
A.
by executing the ALTER SYSTEM … command
B.
by re-creating the control file with a new value for UNDO_RETENTION
C.
by executing the ALTER DATABASE … command in the MOUNT state
D.
by executing UPDATE … statement on V$PARAMETER to change the value of UNDO_RETENTION