Your database instance is configured with automatic undo management and the UNDO_RETENTION parameter is set to 900 seconds. You executed the following command to enable retention guarantee： SQL> ALTER TABLESPACE undotbs1 RETENTION GUARANTEE； What effect would this command have on the database（）

• A、The extents in the undo tablespace retain data until the next full database backup.
• B、The extents containing committed undo in the undo tablespace are not overwritten for at least 15minutes.
• C、The extents containing committed data in the undo tablespace are not overwritten until the instance isshut down.
• D、The extents containing committed undo in the undo tablespace are transferred to Flash Recovery Areabefore being overwritten.