Explanation:
You need to use UNCATALOG clause to remove references to files that no longer exist.
Incorrect Answers:
1: REMOVE clause will not remove references to files that no longer exist.
2: DELETE clause will not remove references to files that no longer exist.
4: There is no CATALOG REMOVE clause in RMAN exists.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 625
Chapter 13: Using Recovery Manager for Backups

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