Answer;
A) respiration of living organisms.
D)absorption of CO2 from the atmosphere by ocean water.
Explanation;
-The level of carbon dioxide in the atmosphere is maintained by several processes, including photosynthesis, respiration and combustion.
-Green plants remove carbon dioxide from the atmosphere by photosynthesis. Living organisms - including all plants and animals - release energy from their food using respiration. Respiration and combustion - burning - both release carbon dioxide into the atmosphere.