Which three conditions must be true for unused block compression to be used automatically while performing backups by using RMAN? 

Answer options:

A. The compatible initialization parameter is set to 10.2 or higher.
B. There are no guaranteed restore points defined for the database.
C. The default device for the backup must be set to disk.
D. The tablespaces are locally managed.
E. The fast recovery area is less than 50 percent free.

ABD

Reference: http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmcncpt.htm#BRADV89481 (See unused block compression) https://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmcncpt.htm#BRADV89481