Question

read the text.
eutrophication, part of the natural aging process for bodies of water such as ponds or lakes, occurs due to a buildup of nitrates and phosphates over time. these compounds, often found in fertilizers, are plant nutrients that stimulate the growth of plants and algae in the water. as the amount of plant matter in the pond increases, more plants start to die off. bacteria that decompose the dead plants also consume the oxygen in the water, so fish and other water animals soon die for lack of oxygen. the pond eventually becomes choked with plant matter and grows shallower. ultimately, as shrubs grow where water once was, the pond dies.
which organizational structure does this text primarily use?
problem - solution
cause - effect
compare - contrast

Explanation:

The text describes eutrophication. It first presents the cause (buildup of nitrates and phosphates). Then it shows a series of effects: growth of plants and algae, plants dying off, bacteria consuming oxygen, fish and water animals dying, pond becoming choked and shallower, and finally the pond dying. This follows a cause - effect structure. There is no problem - solution (no solution presented for eutrophication) or compare - contrast (no comparison of two things) in the text.

Answer:

cause - effect