Which THREE are true about using flashback database in a Data Guard environment?

Flashback Database is a feature that allows reverting a database to a previous point in time, which is

extremely useful in various Data Guard configurations:

It may be used to flash back a physical standby that receives redo from a far sync instance (C):

Flashback Database can be used on a physical standby database to revert it to a past point in time,

even when it is receiving redo data from a far sync instance. This can be particularly useful to recover

from logical corruptions or unwanted changes.

You can use it when real-time apply is enabled in case the physical standby suffers from logical

corruption (D): Even when real-time apply is enabled, which allows redo data to be applied to the

standby database as soon as it is received, Flashback Database can be used to revert the physical

standby database to a point in time before the logical corruption occurred.

It may not be used to flash back a primary database after a failover to a physical standby (E): After a

failover has occurred from a primary to a physical standby database, making the standby the new

primary, Flashback Database cannot be used to revert the old primary database to a state before the

failover because the failover operation makes irreversible changes to the database role and

configuration.

Reference:

Oracle Database Backup and Recovery User's Guide

Oracle Data Guard Concepts and Administration