When using the configuration files that are included with IBM Tivoli Netcool/OMNIbus to create a collection layer ObjectServer and collection to aggregation gateway, how are events removed from the collection layer ObjectServer?

When using the configuration files that are included with IBM Tivoli Netcool/OMNIbus to create a collection layer ObjectServer and collection to aggregation gateway, how are events removed from the collection layer ObjectServer?
A . A database trigger in the collection ObjectServer deletes the events based on the SELECT operations from the gateway.
B . The gateway updates a custom event column after the event is sent to the aggregation layer ObjectServer, and a trigger removes the events based on the value of the column.
C . A signal trigger in the collection ObjectServer deletes the events based on receipt of a signal from the aggregation layer ObjectServer.
D . The gateway deletes the events after they are forwarded to the aggregation layer ObjectServer.

Answer: D