To monitor the health and performance of stream processing in a data pipeline, you should focus on the number of events processed and the processing latency in Azure Functions. This will give you insights into the efficiency and speed of the stream processing. Option B is related to the capacity and throughput of Event Hubs, but it does not directly measure the performance of stream processing. Option C is related to the performance of the Azure Functions service itself, not the stream processing. Option D is related to the connectivity of Azure Functions, but it does not provide insights into the performance of stream processing.