A.The system change number, which is a point in time relative to transactions within a given database. 
B.A number that represents time. Thus, at 1300 hours, the SCN is the same on all databases. 
C.The security change number, which represents the security code that is needed to access any database structure.
D.A conversion factor that converts internal database time to external clock time. 
E.UTC time in the database, providing a standardized way of tracking time in Oracle.