Respuesta :
The independent variable is the water temperature because it is not dependent on the change of another variable so the answer would be D
Answer: D. water temperature
Explanation:
An independent variable is the something which can be altered or manipulated while doing an experiment so as to determine the effect of such change over the other variable that is the dependent variable or the experimental variable.
Here, in the given experiment the water temperature is the independent variable whose effect can be observed on the dependent variable that is the average water flea heart rate.