They have also observed the growth of plantlike organisms in the bay. which
is the most likely explanation for the results?

a. the apple orchard releases toxic chemicals into the water of the
bay.
b. the nitrogen from the fertilizer makes it impossible for plants to
grow.
c. the plantlike organisms generate too much oxygen, which kills the
fish
d. the nitrogen from the fertilizer made the plants grow too quickly,
which hurt the fish.

Explanation:

Well although this isn't a answer provided, it was the correct answer for the same question. The plants aka the apple orchard are using up the oxygen which is needed by the fish, thus causing the population to decrease from lack of oxygen in the water.

"d.) carbon dioxide and hydrogen sulfide"

some fungi obtain their nutrients from a living host (plant or animal) and are called most biotrophic fungi have fairly narrow host ranges—they are specialized on a limited called rhizomorphs that allow the fungus to grow from one tree to another. ascospores are formed inside a sac-like structure called an ascus. so your answer is a