The statement that accurately compares the social structures of Egypt and Mesopotamia is: "Priests and priestesses were closer to the pharaoh in ancient Egypt."
In ancient Egypt, priests held significant power and influence, often being part of the elite class that included the pharaoh. In contrast, while Mesopotamian priests were also important, the social structure did not elevate them to the same level of closeness to leadership as in Egypt. The other statements are incorrect; for example, scribes were part of the educated class, enslaved people were not part of the middle class, and the importance of merchants varied between the two civilizations.