You are operating the IoT infrastructure of a chemical plant where devices are used to ensure that critical valves built-in outdoor pipelines are free from frost. In normal weather conditions, the devices operate as planned, but in unexpectedly and extremely cold weather, the extra heater of some valves must be turned on remotely, with immediate acknowledgment from the device. 
Which of the following solutions should you use?

Answer options:

A.Send a C2D message to the heater
B.Set the extraHeating desired property of the device twin “On”
C.Set the extraHeating tag of the device twin “On”
D.Invoke the extraHeating method of the device

Correct Answer: A
Option A is CORRECT because, with IoT hub’s routing capability, you can forward incoming messages to other Azure services as custom endpoints, like Blob Storage or Service Bus. Enrichment of message also can be applied as part of the routing.
Option B is incorrect Azure Service Bus (both topics and queues) are possible custom endpoints for IoT Hub, hence they are valid targets in message routing.
References: 

https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-endpoints#custom-endpoints
https://docs.microsoft.com/en-us/azure/iot-hub/tutorial-message-enrichments