A. A list of SQL statements and recommendations for tuning
B. A list of SQL statements that have been tuned by the Advisor，with before and after metrics 
C. Graphs showing the actual performance improvement made by the Advisor after it implemented the recommended changes
D. All of the above

A. The command produces an error because the retention period cannot be reduced
B. All historical data older than 3 years is purged from the flashback archive FLA1
C. All historical data is retained but the subsequent flashback data archives are maintained for only 3 years
D. All historical data is transferred to flashback logs and the flashback archive is refreshed to set a new retention time