Explanation:
This command is missing ALLOCATE CHANNEL cname TYPE DISK command. This command is used in conjunction with all major backup, restore, and recovery operations to allow communications between RMAN and the operating system for the purpose of manipulating files.
Incorrect Answers:
1: RESYNC CATALOG command is used to keep the recovery catalog in line with the production database. This command is executed automatically when a database is registered and after a backup, recovery, or restoration.
2: RELEASE CHANNEL command closes the line of communication.
4: SET LIMIT CHANNEL command is used to limit to the size of channel.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 623-625
Chapter 13: Using Recovery Manager for Backups

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