Answer:
B. Hypoxia, or low levels of oxygen
Step-by-step explanation:
Nitrogen eutrophication is a process of algae multiplication, common in bodies of water without much movement, such as lakes and dams. Although it means a large amount of organic matter present in water, it can bring several harm to humans and to nature itself.
Nitrogen eutrophication causes algae pollution in water bodies. This pollution creates a green curtain on the surface of the water body, preventing the passage of light. Thus, plants at the bottom cannot do photosynthesis and the level of dissolved oxygen becomes lower and lower, causing the death of many organisms, such as fish, for example.
In other words, eutrophication causes hypoxia, or low oxygen levels.