You are operating an IoT solution which collects sensor data from a wide range of field devices, including speed sensors, cameras etc. The data is distributed over four IoT Hubs. In order to ensure smooth operation, you want to set up a monitoring and alert solution. You want to prevent loss of messages, and to get alerted when your daily quota for your hubs is exhausted to a certain level. You have the choice of the following steps to build the solution: Create action group with notification
Add diagnostic setting: Device telemetry
Set metric: Telemetry messages sent
Create alert rule
Set metric: Total number of messages used
Which of the above steps should you execute?

Answer options:

A.1, 4, 5
B.2, 3, 4
C.2, 4, 5
D.3, 4, 5

Correct Answer: A
Option A is CORRECT because in order to get an email alert in this scenario, you need to create an alert rule for Total number of messages used metric, and an action group with email notification must be created.
Option B is incorrect because diagnostic settings are not needed for the given scenario; the Total number of messages used is the appropriate metric here.
Option C is incorrect because diagnostic settings are not needed for alerts; they are useful for sending the logs collected on the IoT Hub to external services like Log Analytics.
Option D is incorrect because it is the Total number of messages used metric that holds the aggregate number of messages, relevant for controlling the quotas. Telemetry messages sent is useful to monitor message throughput, to prevent throttling, for example.
Reference: 

https://docs.microsoft.com/en-us/azure/iot-hub/tutorial-use-metrics-and-diags#set-up-metric-alerts