D makes more sense. The source of truth is always the repo. C is going to cause stress and complications when merging newer developments.

I might have misunderstood in this question. But D does not mention about next sprint strategy.

D is not correct. A should be correct. What does "All fixes must be made in the release branch" means in this situation?
All fixes come from new sprint? Usually to begin next spring, new feature branch should be created from developer branch. They can start next spring in feature branch.
Moreover, if current sprint changes are not approved and need to be fixed, they must be fixed in developer branch and create release branch again and deploy to production. If release branch is not created, they could deploy from developer branch.

My selection is that D should be the correct answer

Yes D is the correct answer. C cannot be correct

no way it is C, since you don't want your source of truth to be org-based if there are alternative answers.
A and D are equivalents, basically. but D talks about managing fixes in testing and down the gitflow, so I would say D is correct.