Imagine that you wish to compare two different diets that will be fed to tadpoles raised in a lab. One diet is a meat-based fish food, and the other is the traditional diet of boiled lettuce. You want to see if the meat-based diet will be associated with an increase in the average weight of the tadpoles. In your experiment you keep all other factors, such as tadpole density per pan, temperature, pH, and the amount of food the same. The only difference between your control and experimental groups is the type of food the tadpoles receive. What is the independent variable for the tadpole diet experiment?