You noticed that the current value of the UNDO$\_$RETENTION parameter is $900$ and is too low for some of your transactions. The database was created using DBCA. Which is true if you issue the following SQL statement:

ALTER SYSTEM SET UNDO$\_$RETENTION$=4800$

A$.$

UNDO$\_$RETENTION is a static parameter and, therefore, cannot be changed using ALTER SYSTEM.

B$.$

The change will be available to the instance onl after a database cycle..

C$.$

The value is changed in memory, and when the database restarts the next time, the new value will be preserved when using the spfile.

D$.$

The value is changed only in memory, and the server parameter file needs to be updatedd for the change to persist across database shutdowns.