Answer:
A. humans going underwater and exhaling
Explanation:
Dissolved oxygen is the oxygen content that can be found in a water body. Oxygen is a gaseous component that dissolves readily in water, however, oxygen dissolves in water via the following sources including diffusion from the atmosphere, aeration as water moves over rocks and debris, and from wind and wave, photosynthesis of aquatic plants.
Humans like every other living organism will undergo cellular respiration and release CO2 (carbon dioxide gas) as a a product during exhalation. Hence, humans going underwater and exhaling cannot be a source of dissolved oxygen.
