Yes, I am confident that option C is the most accurate choice regarding the uniqueness of priests in Sumerian society. They were indeed seen as intermediaries who communicated with the gods on behalf of the people. While there were female priestesses as well, the key role of priests in connecting the divine with the community is a notable characteristic of their function in Sumer.
However, it is worth noting that options A and B can also represent aspects of priestly roles in certain contexts, though they are not as universally defining as option C. Would you like more detailed information on any of those points?