A Carrying capacity is reached for the Paramecium population but not the Daphnia population.

B
Carrying capacity is reached for both the Paramecium population and the Daphnia population.

C
Both the Paramecium population and the Daphnia population fluctuate over time and never stabilize.

D
Both the Paramecium population and the Daphnia population continue to increase over time.

B . Carrying capacity is reached for both the Paramecium population and the Daphnia population.

Explanation:

Carrying capacity is reached for both the Paramecium population and the Daphnia population because there is no increase occur in the population of both Paramecium and the Daphnia. When there is no further increase occur in the population of an organism, it means that it reaches to its carrying capacity.  Carrying capacity is the maximum population size of a species that can be sustained by that specific environment which depends on the resources of that environment.

answer; being clearly political;