You have a Microsoft 365 subscription and responsible for delegating access to your users. In your subscription you have a resourcegroup called RG-Development, of which all developers in your company have RBAC Contributor rights. A developer sends you a mail stating that he has no longer access to create any services in the resource group. You verify that he now only has Reader rights. You need to investigate who changed the access level. Where should you look? 

Answer options:

A.Azure Active Directory – Sign-ins
B.In the resourcegroup blade – Access Control – Check access
C.In the resourcegroup blade – Tags
D.In the resourcegroup blade – Activity log

Correct Answer: D 
You can view any changes made to the access control in Activity log for the selected resource group for the past 90 days, in this case RG-Development.
Option A is incorrect. The Azure AD sign-in view lets you dig in to details about how your users are signing in to Azure and Office 365.
Option B is incorrect. The access control – Check access view lets you view the current access levels on the resource, but not changes that have been previously made.
Option C is incorrect. The resource Tags lets you logically organize your resources into a taxonomy. 
Reference: 
To know more about using the activity log, please refer to the link below: 

https://docs.microsoft.com/en-us/azure/role-based-access-control/change-history-report