Why would you run the delete obsolete command?

Why would you run the delete obsolete command? (Choose all that apply.)

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

Explanation:
Deleting Expired RMAN Backups and Copies
If you run CROSSCHECK, and if RMAN cannot locate the files, then it updates their records
in the RMAN repository to EXPIRED status. You can then use the DELETE EXPIRED
command to remove records of expired backups and copies from the RMAN repository.
The DELETE EXPIRED command issues warnings if any files marked as EXPIRED actually
exist. In rare cases, the repository can mark a file as EXPIRED even though it exists. For
example, a directory containing a file is corrupted at the time of the crosscheck, but is later
repaired, or the media manager was not configured properly and reported some backups as
not existing when they really existed.
To delete expired repository records:
If you have not performed a crosscheck recently, then issue a CROSSCHECK command.
For example, issue:
CROSSCHECK BACKUP;
Delete the expired backups. For example, issue:
DELETE EXPIRED BACKUP;
Deleting Obsolete RMAN Backups Based on Retention Policies
The RMAN DELETE command supports an OBSOLETE option, which deletes backups that
are no longer needed to satisfy specified recoverability requirements. You can delete files
that are obsolete according to the configured default retention policy, or another retention
policy that you specify as an option to the DELETE OBSOLETE command. As with other
forms of the DELETE command, the files deleted are removed from backup media, deleted
from the recovery catalog, and marked as DELETED in the control file.
If you specify the DELETE OBSOLETE command with no arguments, then RMAN deletes all
obsolete backups defined by the configured retention policy. For example:
DELETE OBSOLETE;