What part of a Mule flow can contain a Poll scope?

• A. Flow reference
• B. Sub-flow
• C. Message source
• D. Message processor

Answer: (C)

The Poll scope is a message source. It provides the trigger that starts processing by polling a data source and emitting messages into the flow. In Mule, the message source is what initiates a flow by delivering the initial event; the Poll scope serves that role by periodically producing messages to process.

Why the others don’t fit: a flow reference simply routes control to another flow and isn’t a data source. A sub-flow is a reusable group of processors, not what starts the flow by pulling data. A message processor acts on a message inside the flow after it’s started; the poll scope’s job is to initiate the flow by generating messages, not to process them.