You have an Azure Virtual Desktop host pool and you need to add session hosts to it. Which of the following is the necessary step you must take before adding session hosts to the host pool?

Answer options:

A.Creating a registration key for the workspace
B.Creating a registration key for the session host
C.Creating a registration key for the host pool
D.Creating a registration key for the application group

Correct Answer: C 
Registration key/token is created for the host pool to authorize the session hosts to join the host pool. New-AzWvdRegistrationInfo is the cmdlet that is used in PowerShell to create the registration key.
Option A is incorrect.The registration key is created at the host pool, not the workspace.
Option B is incorrect. The registration key is not created for the session host. Rather, it is created at the host pool.
Option C is correct. The registration key is created at the host pool.
Option D is incorrect. The registration key is created at the host pool, not the application group.
Reference: 
To know more about how to create an Azure Virtual Desktop host pool with PowerShell, please visit the below-given link: 

https://docs.microsoft.com/en-us/azure/virtual-desktop/create-host-pools-powershell?tabs=azure-powershell