Why would you run the delete obsolete command？（）  

• A、 To remove missing backup set pieces physically from disk
• B、 To remove metadata related to backup set pieces in the control file and the recovery catalog
• C、 To mark as deleted records in the control file and the recovery catalog associated with obsolete backup sets
• D、 To delete backup set pieces associated with backups that are no longer needed due to retention criteria
• E、 To remove old versions of RMAN backups