What does the SCN represent?（）

• 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.