To enable faster incremental backups， you enabled block change tracking for the database. Which two statements are true about the block change tracking file？（） 

• A、 Multiple change tracking files can be created for a database.
• B、 The change tracking file must be created after the first level 0 backup.
• C、 RMAN does not support backup and recovery of the change tracking file.
• D、 The database clears the change tracking file and starts tracking changes again，after whole database restore and recovery operations.