Which three are true about monitoring waits for sessions and services? (Choose three.)

[answerhappygod]

Which three are true about monitoring waits for sessions and services? (Choose three.)

A. V$SESSION_EVENT displays all waits for all past and existing sessions if the wait has occurred at least once for a session.
B. V$SERVICE_EVENT displays all waits for all services if the wait has occurred at least once for a service.
C. V$SESSION_WAIT_CLASS displays waits broken down by wait class only for waiting sessions.
D. V$SESSION_WAIT and V$SESSION both contain details of the event on which a non-waiting session last waited. E. V$SESSION_EVENT displays all waits for all past sessions if the wait has occurred at least once for a session. F. V$SESSION_WAIT and V$SESSION both contain details of the event on which a session is currently waiting.