Which two are prerequisites for performing a flashback transaction?（）
- A Flashback Database must be enabled.
- B Undo retention guarantee for the database must be configured.
- C EXECUTE privilege on the DBMS_FLASHBACK package must be granted to the user flashing back transaction.
- D Supplemental logging must be enabled.
- E Recycle bin must be enabled for the database.
- F Block change tracking must be enabled tor the database.