Answer:
Acid rain
Step-by-step explanation:
The independent variable in the hypothesis statement is the acid rain. An independent variable is usually the cause in an experiment.
This variable give rises to the effects observed as the dependent variable.
In the presence of the acid rain, the fish population will increase.
The dependent variable is the fish population or number of fishes.
The independent variable is the acid rain as it is the cause of the effect observed on the fish population.