You work as a database administrator for Supportcenter.cn. You are using Recovery Manager （RMAN） to perform backups in your databases. Which four backup operations can be performed using RMAN？（）

• A、A backup of the target database when it is mounted
• B、A backup of online redo log files when the database is open
• C、A backup of only used data blocks in the file beingbeingbackup up
• D、A backup of online， read/write data files when the database is open
• E、A backup of only those data blocks that have changed since a previous backup
• F、A backup of online， read/write data files when the database is in the NOMOUNT state.