160.Which two statements are true about the duplexing of the backups taken by RMAN? (Choose two.)
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
Answer: BD

参考：http://blog.csdn.net/rlhua/article/details/14441471

RMAN can duplex backups to either disk or tape, but cannot duplex backups to tape and disk simultaneously.