Which three are true about thresholds, metrics, and server-generated alerts? (Choose three.) 

Answer options:

A. All metrics are instance related.
B. Cleared stateful alerts are displayed by querying DBA_ALERT_HISTORY.
C. A space usage management alert is automatically cleared after the underlying problem is resolved.
D. They are generated by SMON when a tablespace is 97% full.
E. Metrics are statistical counts for a specific unit.
F. STATISTICS_LEVEL must be set to ALL to generate alerts.

CEF

Reference: https://docs.oracle.com/cd/E11882_01/server.112/e41573/autostat.htm#PFGRF027 https://blogs.oracle.com/oem/how-to-clear-an-alert-v2