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