Answer: A. how shiny each mouse's fur is
Step-by-step explanation:
In experimental procedure, the independent variable in the experiment is the variable which can be altered, manipulated or changed in order to observe the impact of this process over the dependent variable which is the result of the experiment.
A. is the correct option as it depends upon the amount of food he feeds a mouse. More clearly, here food is the independent variable and shiny fur is the dependent variable.