Which two statements are true about the duplexing of the backups taken by RMAN？（）  

• A、 It’s only supported for the backups performed on the tape
• B、 It is not supported for backup operations that produce image copies
• C、 Duplex backups need a parallelism for the device to be equal to number of copies
• D、 Duplex backups can be performed to either disk or tape， but cannot be performed on tape and disk simultaneously