Answer: D. Colors of peppered moths
Step-by-step explanation:
In an experimental set up, an independent variable can be changed either by it's own or manually. This change can be observed over the dependent variable. The changes in the dependent variable can be observed so as to determine the outcome of the experiment.
The independent variable is the test variable of the experiment and the dependent variable is the experimental variable.
According to the condition, the color of the peppered moths is the independent variable, as it's affect is to be determined over the survival rate of the peppered moths which is the result of the experiment. The color may vary among the peppered moths.