Explanation:
This command sets retention policy to the default of REDUNDANCY 1.
Incorrect Answers:
1: This command does not mean that backup will never expire.
2: It sets the retention policy to the default of REDUNDANCY 1, does not remove any retention policy.
3: The DELETE OBSOLETE command will not fail after that command.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 182-189
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 79-84
Chapter 3: New Oracle9i Availability and Recoverability Features

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