Explanation:
Command CATALOG is used to update recovery catalog about files created before RMAN and about operating systems backup. A datafile image copy, backup control file, or archived redo log taken using methods other than RMAN can be used by RMAN if it is identified to the recovery catalog with the CATALOG command. Only files that are part of the database can be part of the recovery catalog for that database.
Incorrect Answers:
1: RMAN recovery catalog does not work with rollback segments itself.
4: Only Oracle8 files can be cataloged, RMAN recovery catalog does not work with earlier versions of Oracle.
5: Both the target database and the recovery catalog must be defined for this operation to work. This command does not work with the clone database.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 625
Chapter 13: Using Recovery Manager for Backups

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