Which two statements are true regarding undo data records?

A.
They are required to support Flashback features.

B.
They are not required if Flashback features are enabled.

C.
They are retained until the session making the changes ends.

D.
Undo records contain copies of data as it appears after a change is made.

E.
Undo records contain copies of data as it appears before a change is made.

Explanation:
http://docs.oracle.com/cd/E11882_01/server.112/e25494/undo.htm#ADMIN11463