An experiment is designed to examine the causes of colon cancer. All rates housed in cages maintained at 25oC, with 16 hrs of light/day. They are provided 1 hour of exercise/day and have unlimited access to water. In group A, rats are fed a diet of 100 calories/day consisting of 60% fat, 10 % protein, 10% fiber and 20% carbohydrates. In group B, rats are fed a diet of 100 calories/day consisting of 20% fat, 10 % protein, 10% fiber and 60% carbohydrates. The amount of light each day is: a. The dependent variable
b. The independent variable
c. A control variable
d. The experimental variable