Explanation:
Scripts run by the Agent in any language on the host server are user defined events. You have the capability to create custom scripts via the Diagnostic Pack that monitor conditions that you specify.
Incorrect Answers:
1: Database based scripts (PL/SQL, Java) run by the Agent are not user defined events.
2: Database Event Triggers, which issue Alerts to the Agent, are not considered as user defined events.
4: Scripts run by the Agent in any language on the host server, not user written PL/SQL programs in the database, are user defined events.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 189-201
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 219-220
Chapter 7: Oracle9i Real Application Clusters

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