Which two statements about Flashback Query are true？（）

• A、It is generated by using the redo log files. 
• B、It helps in row-level recovery from user errors.
• C、It can be performed to recover ALTER TABLE statements 
• D、It fails when undo data pertaining to the transaction is overwritten.
• E、The database has to be opened with the resetlogs option after performing Flashback Query.