Which statement is true about a Scheduler-generated event?

Which statement is true about a Scheduler-generated event?

A.
It can be generated when a file arrives on the file system.

B.
it indicates state changes that occur within the Scheduler itself.

C.
it is raised by an application that is consumed by the Scheduler to start a job.

D.
it requires jobs to be defined with an event condition and a queue specification.

Explanation:
Consuming Job State Events with your Application
To consume job state events, your application must subscribe to the Scheduler event queue
SYS.SCHEDULER$_EVENT_QUEUE. This queue is a secure queue and is owned by SYS.
To create a subscription to this queue for a user, do the following:
1. Log in to the database as the SYS user or as a user with the MANAGE ANY QUEUE
privilege.
2. Subscribe to the queue using a new or existing agent.
3. Run the package procedure DBMS_AQADM.ENABLE_DB_ACCESS as follows:

DBMS_AQADM.ENABLE_DB_ACCESS(agent_name, db_username); where agent_name
references the agent that you used to subscribe to the events queue, and db_username is
the user for whom you want to create a subscription.
There is no need to grant dequeue privileges to the user. The dequeue privilege is granted
on the Scheduler event queue to PUBLIC.