Question

lake erie is home to a form of algae called \cyanobacteria.\ this species can produce the toxin microcystin, which poses a risk to human and wildlife health. the cells that produce this toxin sometimes float to the surface of water, while at other times they sink to the bottom. because water treatment intake structures are usually located below the surface, the risk of toxins in raw water may be greater when these cells sink. in the summer of 2020, despite an unusually large toxic bloom, water treatment facilities reported little to no instances of toxic water intake. this suggests that
which choice most logically completes the text?
a a toxic bloom did not occur that summer, despite scientists fears.
b more cyanobacteria gathered near the bottom of the lake than at the surface that summer.
c cyanobacteria generally floated at the surface of the water that summer instead of sinking to the bottom.
d cyanobacteria produced significantly lower levels of microcystin that summer because of scientists protective measures.

Explanation:

The text states that the risk of toxins in raw water is greater when the cyanobacteria cells sink, and despite a large toxic bloom in 2020, there were few toxic water - intake instances. This implies that the cyanobacteria did not sink as much, meaning they generally floated at the surface. Option A is incorrect as a toxic bloom did occur. Option B would increase the risk of toxic water intake. Option D has no basis in the given text about scientists' protective measures reducing toxin levels.

Answer:

C. cyanobacteria generally floated at the surface of the water that summer instead of sinking to the bottom