I would say C is the most correct.
In D it depends on what water source you're using. Let's say it is a waterfall, then the source of the water (melting ice or a lake) may disappear in the future.
If you're using underwater "windmills" placed in the ocean, then you would expect it to last a while as the ocean will not disappear in the near future.
I believe the answer is D
Answer: balanced chemical equation: 
Net ionic equation :
Explanation:
A double displacement reaction is one in which exchange of ions take place. The salts which are soluble in water are designated by symbol (aq) and those which are insoluble in water and remain in solid form are represented by (s) after their chemical formulas.
The balanced chemical equation is:

Spectator ions are defined as the ions which does not get involved in a chemical equation or they are ions which are found on both the sides of the chemical reaction present in ionic form.
The ions which are present on both the sides of the equation are sodium and nitrate ions and hence are not involved in net ionic equation.
Hence, the net ionic equation is
Answer:
Water near the poles often have higher salinity because Cold polar air cools the water and lowers its temperature, increasing its salinity. Fresh water freezes out of seawater to become sea ice, which also increases the salinity of the remaining water.
Understands! ♥
When a solid (solute) comes in contact with the liquid (solvent), the solute goes about C) dissolution, in which the solid dissolves into the liquid.
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