Which two are prerequisites for performing a flashback …

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.

Explanation:
http://searchoracle.techtarget.com/tip/How-to-perform-Oracle-Flashback-Transaction-Queries
https://docs.oracle.com/cd/E11882_01/appdev.112/e41502/adfns_flashback.htm#ADFNS610