答案bc
B正确：When RMAN first detects missing or corrupt redo records during block media recovery, it does not immediately signal an error because the block undergoing recovery may create a new one later in the redo stream.
C正确：Whenever block corruption has been automatically detected, you can perform block media recovery manually with the RECOVER ... BLOCK command. By default, RMAN first searches for good blocks in the real-time query physical standby database, then flashback logs and then blocks in full or level 0 incremental backups.
http://docs.oracle.com/cd/E25054 ... lock.htm#BRADV89781
