Explanation:
To verify the existence of backups (backup sets or media-managed proxy copies) and copies (both archived logs and image copies) stored on disk or tape. The CROSSCHECK command only processes files created on the same device type as the channels running the crosscheck. Incorrect Answer:
1: The CHANGE command is used to change the status of backups, copies, and archived logs in the repository to AVAILABLE or UNAVAILABLE.
2: The RESYNC command performs a full resynchronization of the recovery catalog.
3: This command is used for RMAN catalog creation.
Reference:
OCP Oracle 9i Database: Fundamentals II Exam Guide, Rama Velpuri, p. 269-270
Chapter 11: RMAN Backups

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