You are operating an IoT solution which collects sensor data from a wide range of field devices, including speed sensors, cameras etc. You have configured several message routes depending on the telemetry data and on the geographical location of the devices. In order to ensure smooth operation, you want to set up a solution to log all routing related metrics so that you can visualize and analyze them using Azure tools. 
What settings should you make in the IoT Hub?

Answer options:

A.Metrics / Routing: <metrics>
B.Diagnostic settings / Send to Log Analytics workspace
C.Diagnostic settings / Stream to an event hub
D.Logs / Send to Log Analytics Workspace

Correct Answer: B
Option A is incorrect because IoT Hub / Metrics is for setting up charts and dashboards for visualizing selected metrics in order to get real-time insights on the IoT Hub. It is not for setting-up log collection. Use Diagnostic settings instead.
Option B is CORRECT because the best way to collect logs about any device-related events for visualization and evaluation purposes is forwarding them to an Azure Log Analytics workspace. In order to connect your IoT Hub to a LA workspace, a diagnostic setting must be defined. The log category (in this case: “Routes”) must also be selected.
Option C is incorrect because while the log data can be forwarded to Event Hubs, it is recommended for scenarios where the data is to be analyzed by external applications.
Option D is incorrect because IoT Hub / Logs is for querying and analyzing logs that have been collected before. It is not for setting-up log collection. Use Diagnostic settings instead.
References: 

https://docs.microsoft.com/en-us/azure/iot-hub/tutorial-use-metrics-and-diags
https://docs.microsoft.com/en-us/azure/iot-hub/monitor-iot-hub-reference
https://docs.microsoft.com/en-us/azure/iot-hub/monitor-iot-hub