You have to build an IoT solution which gathers data from 400 devices, with the expected total load of 100000 messages per day. Most of the devices are smart sensors, ready to connect to the IoT Hub, but some of them need to be connected via Linux-basedgateway devices. You want to use advanced configurations to control the devices remotely and to distribute some logic to the edges. There are also some low resource, legacy temperature sensors which must be directly connected to the Hub and need to communicate through port 443. 
Which communication protocol would you use for which device category?

Answer options:

A.Smart sensors - MQTT; Gateway - AMQP ; Temp sensors - AMQP
B.Smart sensors - MQTT; Gateway - AMQP ; Temp sensors - HTTPS
C.Smart sensors - MQTT; Gateway - MQTT; Temp sensors - HTTPS
D.Smart sensors - MQTT; Gateway - MQTT over WebSockets; Temp sensors - HTTPS

Correct Answer: B
Option A is incorrect because for low-resource devices, the AMQP protocol is not the right choice. For these, “legacy” devices often the HTTPS is the only choice, because of its smallest footprint.
Option B is CORRECT because MQTT is common for new types of sensors; AMQP is the only supported option for gateway devices; HTTPS is the right option for low-resource devices which are allowed to connect to port 443 (note: MQTT over WebSockets could also be a valid option).
Option C is incorrect because gateway devices will be used to connect several single devices to the IoT Hub. Forwarding traffic from multiple sources with multiple IDs requires using the AMQP protocol. Selecting MQTT for the gateway devices is not supported.
Option D is incorrect because gateway devices will be used to connect several single devices to the IoT Hub. Forwarding traffic from multiple sources with multiple IDs requires using the AMQP protocol. Neither MQTT nor MQTT over WebSockets for gateways are supported.
Reference: 

https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-protocols