Explanation:
You can switch undo tablespaces from the current one, called UNDO1, to a new one called UNDO2. Only current active transactions will continue to execute inside UNDO1, all new transactions will be assigned to the new undo tablespace.
Incorrect Answers:
1: You can switch undo tablespaces while active transactions will run in the old undo tablespace. All new transactions will be assigned to the new undo tablespace.
2: Current active transactions will abort if you switched undo tablespaces.
3: Current active transactions will continue to execute inside UNDO1 till they commit or roll back. They will not be automatically migrated to UNDO2.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 160-166
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 19-25
Chapter 1: Oracle9i Database Administration and Management Features

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