Box 1: Reader -
Members of the Reader role can view the organization agent pool as well as agents. You typically use this to add operators that are responsible for monitoring the agents and their health.
Box 2: Service account -
Members of the Service account role can use the organization agent pool to create a project agent pool in a project. If you follow the guidelines above for creating new project agent pools, you typically do not have to add any members here.
Incorrect Answers:
In addition to all the permissions given the Reader and the Service Account role, members of the administrator role can register or unregister agents from the organization agent pool. They can also refer to the organization agent pool when creating a project agent pool in a project. Finally, they can also manage membership for all roles of the organization agent pool. The user that created the organization agent pool is automatically added to the Administrator role for that pool.
Reference:
https://docs.microsoft.com/en-us/azure/devops/pipelines/agents/pools-queues
