(Choose all that apply.)

Identify the scenarios in which the RMAN CROSSCHECR command is useful. (Choose all
that apply.)

A.
To check that the obsolete backups are deleted from the repository records and from the
disk.

B.
To update the RMAN repository if you delete archived redo logs with operating system
commands.

C.
To update outdated information about backups that disappeared from disk or tape or
became corrupted and inaccessible.

D.
To synchronize the actual files on disk or in the media management catalog with the
RMAN repository for which the backup was not taken using RMAN.

Explanation:
Crosscheck are useful because they can do the following: (Link)
Update outdated information about backups that disappeared from disk or tape or became
corrupted
Update the repository if you delete archived redo logs or other files with operating system
commands
Use the CROSSCHECK command to synchronize the physical reality of backups and copies
with their logical records in the RMAN repository.
The CROSSCHECK command checks only objects marked AVAILABLE or EXPIRED in the
repository by examining the files on disk for DISK channels or by querying the media
manager for sbt channels.
Meaning of Crosscheck Status:
EXPIRED
Object is not found either in file system (for DISK) or in the media manager (for sbt). A
backup set is EXPIRED if any backup piece in the set is EXPIRED.
The CROSSCHECK command does not delete the repository records of the files that it does
not find, but updates their repository records to EXPIRED. You can run DELETE EXPIRED
to remove the repository records for expired files and any existing physical files whose status
is EXPIRED.
If backups are EXPIRED, then you can re-execute the crosscheck later and determine
whether expired backups are available. This precaution is especially useful when you use
RMAN with a media manager. For example, if some backup pieces or copies were
erroneously marked as EXPIRED because the PARMS channel settings were incorrect, then
after ensuring that the files really do exist in the media manager, run the CROSSCHECK
BACKUP command again to restore those files to AVAILABLE status.
AVAILABLE
Object is available for use by RMAN. For a backup set to be AVAILABLE, all backup pieces
in the set must have the status AVAILABLE.