You create a table with the PERIOD FOR clause to enable the use of the Temporal Validity feature of Oracle Database 12c. Examine the table definition: Which three statements are true concerning the use of the Valid Time Temporal feature for the EMPLOYEES table?（）

• A、The valid time columns employee_time_start and employee_time_end are automatically created.
• B、The same statement may filter on both transaction time and valid temporal time by using the AS OF TIMESTAMP and PERIOD FOR clauses.
• C、The valid time columns are not populated by the Oracle Server automatically.
• D、The valid time columns are visible by default when the table is described.
• E、Setting the session valid time using DBMS_FLASHBACK_ARCHIVE.ENABLE_AT_VALID_TIME sets the visibility for data manipulatio