What should you look at first to compute the number of undo blocks written per second to disk？ （）

A.A
B.B
C.C
D.D

A.Oracle Flashback uses undo information to construct consistent data. 
B.You can use a cursor opened while using an Oracle Flashback image to perform DML once you deactivate Oracle Flashback in your session. 
C.You can only use Oracle Flashback view of the data if the required records are still in the online redo log files. 
D.Oracle Flashback lists the DML that was executed during the period you identify when initiating your session. 

A.The unit of versioning is the schema.
B.It is possible to version enable a table pertaining to SYS.
C.There are as many segments as versions for the same base table.
D.It is possible to create workspaces if there is no version-enabled table in the database.