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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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出自：Oracle认证

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