Which option correctly uses commas to set off a nonrestrictive clause?

A. Plato who was a Greek philosopher, wrote the tragic story of the ancient civilization Atlantis.

B. Plato who was a Greek philosopher wrote the tragic story of the ancient civilization, Atlantis.

C. Plato, who was a Greek philosopher, wrote the tragic story of the ancient civilization Atlantis.

D. Plato who was, a Greek philosopher, wrote the tragic story of the ancient civilization Atlantis.