---> D

D - is more granular since it provides the right balance of granting necessary permissions while maintaining security and following the principle of least privilege. It allows the developer to create and configure service-linked roles as needed for the proof of concept, while the permissions boundary ensures that they can't exceed their intended level of access.

A. This approach involves creating a user in the management account and setting up cross-account roles, which adds unnecessary complexity and potential security risks. B. PowerUserAccess managed policy provides broad permissions that go beyond just creating and configuring service-linked roles. This approach does not meet the requirement to restrict the developer's capabilities specifically to service-linked role management. C. SCPs are used to set permission guardrails at the organizational or account level, but they do not grant permissions. They are used to restrict actions, and configuring an SCP with a deny rule for iam:* would likely prevent the developer from performing necessary actions D effectively meets the requirements