The correct option is B. "cool, shallow, fresh water". This conditions allow photosynthesis to occur without problems. Shallow waters allow enough light to penetrate the coral's algae symbiont, while cool water allows the photosynthesis enzymes to properly work. If temperatures rises the algae symbiont activity is impaired and it left the coral. If the coral is in deep waters, it will not have enough light, and again, its algae symbiont will suffer the consequences of a diminished photosynthetic radiation exposure.