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 feature