You work at Contoso as an IT admin. You have a Microsoft 365 subscription and an Azure tenant on the Premium 1 tier. Your manager has decided you need to bring in an external consultant from Company A to do a task. The consultant should be able to log in with his username and password from Company A. What should you do?

Answer options:

A.Create a new internal user for the consultant in the Contoso tenant.
B.From Azure AD – Identity governance, create a new catalog.
C.Run from Powershell connected to tenant: New-AzRoleAssignment
D.Run from Powershell connected to tenant: New-AzureADMSInvitation

Correct Answer: D 
You should invite the external consultant as a new guest user in your tenant. This can be done in several ways, for instance in the Azure Active Directory admin portal. Another method is to connect powershell to the tenant domain and run the New-AzureADMSInvitation command.
Option A is incorrect. Creating a new internal user is incorrect. This will not allow him to log in with his Company A username and password.
Option B is incorrect. A catalog is a container of resources and access packages that can be shared with external users. Therefore it is not the correct answer.
Option C is incorrect. This is the powershell-command for creating a new Role assignment.
Reference: 
To know more about guest user invitations, please refer to the link below: 

https://docs.microsoft.com/en-us/azure/active-directory/external-identities/b2b-quickstart-invite-powershell