You have enabled backup optimization for the RMAN environment. Identify two criteria on which RMAN will skip the file， if it has already been backed up.（）
A. The data file backup is done with multiple channels
B. The data files is in the read-write mode after being backed up in the read only mode
C. The backup was taken after the data files was taken offline-normal or is in the read only mode
D. The data file backup complies with the back retention policy and the backup duplexing fe ture
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