Explanation:
It's better to set a data file offline when the database is in MOUNT state to minimize downtime.
Incorrect Answers:
2: This will not help for automatic data file recovery.
3: It's not used to prevent further corruption of a damaged data file.
4: You set a data file offline when the database is in MOUNT state to minimize downtime, not to recover it later.
Oracle 8, DBA Certification Exam Guide, Jason S. Couchman, p. 585-591
Chapter 12: Overview of Backup and Recovery

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