单项选择题 AUM has been retaining about 15 minutes worth of undo. You want to double the retentionperiod， but not at the expense of new transactions failing. You decide to alter the system to set the parameter UNDO_RETENTION=18000. However， AUM still retains only about 15 minutes worth of undo.  What is the problem？ （）

单项选择题 A user named Arren is executing this query：   select table_name，operation，undo_sql  from  flashback_transaction_query t，  （select versions_xid as xid  from employees versions between scn minvalue and maxvalue  where employee_id = 123） e  where t.xid = e.xid；   When the query runs，he receives an ORA-01031： insufficient privileges error. Since the user owns the employees table，you know that it is not the problem.  Which of the following SQL statements will correct this problem？（）

单项选择题 Over the course of a day，a department performed multiple DML statements （inserts， updates， deletes） on multiple rows of data in multiple tables. The manager would like a report showing the time， table name，and DML type for all changes that were made. Which Flashback technology would be the best choice to produce the list？（）