The downstream devices send millions of telemetry data to your standard IoT Hub and all the incoming messages must be processed in the order they occur. You started with an IoT Hub having 1 partition (i.e. no partitioning) but the volume is expected to increase, so, and in order to cope with the huge amount of incoming data, you need to scale up your infrastructure. You have a choice of possible steps to achieve your goal: Set the number of partitions of Hub2 to 8
Set the retention time to 14 days
Create a new IoT Hub (Hub2)
Set the number of partitions of Hub1 to 8
Adjust the processing applications so that the order of events is retained
Migrate traffic from Hub1 to Hub2
Which steps should you take in order to solve the problem?

Answer options:

A.4, 2, 5
B.3, 1, 6
C.4, 5
D.3, 1, 5, 6

Correct Answer: D
Option A is incorrect because the partition count cannot be changed once the Hub is created. The maximum retention time is 7 days and cannot be increased.
Option B is incorrect because when having more than one partition, the events are sent to multiple partitions without retaining the order. A more complex application logic is needed when the order of events must be preserved.
Option C is incorrect because the partition count cannot be changed once the Hub is created.
Option D is CORRECT because the partition count cannot be changed once the Hub is created. Therefore, a second Hub must be created with a higher partition count. The application logic should be adjusted if retaining the order of events is a requirement. And, finally, the traffic must be directed to the new hub.
References: 

https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-scaling#partitions
https://docs.microsoft.com/en-us/azure/event-hubs/event-hubs-faq#how-many-partitions-do-i-need
https://docs.microsoft.com/en-us/azure/event-hubs/event-hubs-features#partitions