The correct answer is D. Both absorb carbon dioxide from the atmosphere.
The process of photosynthesis is carried out using atmospheric carbon dioxide by green plants. Many gases including carbon dioxide are dissolved in seawater. Some of the carbon dioxide gas remains in dissolved state but most of the carbon dioxide is reacts with water to form carbonic acid. Dissolved gases in seawater make balance with atmosphere by mixing of the surface by wind and waves. Therefore, both photosynthesis and sea water take carbon dioxide from the atmosphere.