Hey there! The answer is D, Salinity. Salinity is the concentration of salt in water. Ocean water often has high salinity and this can contribute to things like upwelling and water density- but these all start from salinity. Hope this helps!
Copper(I) sulfate, also known as cuprous sulfate and dicopper sulfate, is the chemical compound with the chemical formula Cu2SO4 and a molar mass of 223.15 So its "Cu2s"