Assigned membership groups require an admin (or automation) to explicitly add users to the group. This does not automatically evaluate user attributes like department. While you could combine assigned groups with scripting, that increases administrative effort and ongoing maintenance compared to dynamic user groups.
ARM templates are used to deploy and manage Azure resources (VMs, VNets, storage, etc.). They are not designed for bulk importing Entra users or implementing attribute-based group membership. This option is a common distractor when the question is actually about identity governance rather than Azure resource deployment.
Dynamic User membership groups automatically include users based on a rule that evaluates user attributes such as department. This directly satisfies the requirement to add imported users to a group based on department and minimizes administrative effort because membership is maintained automatically as attributes change. Note: typically requires Microsoft Entra ID P1.
A PowerShell script could parse an import file and add users to groups, but it introduces extra administrative effort (script creation, testing, permissions, error handling, and ongoing maintenance). The question asks to minimize administrative effort; native dynamic group rules are the more appropriate and scalable approach.
Microsoft Entra bulk user import is typically performed using a CSV template in the Entra admin center. XML is not the standard supported format for bulk user creation in this context. Even if you could transform data into XML for other tooling, it would not be the simplest or expected exam answer.
A CSV file is the standard method for bulk importing users into Microsoft Entra ID via the admin center. By including the Department attribute in the CSV, you enable dynamic group rules to evaluate and automatically assign membership immediately after import. This aligns with the requirement for minimal administrative effort.