A student is conducting their science experiment on the effect of caffeine on
dogs. He has 3 groups of test subjects. The 1st group of dogs receives plain
water. The 2nd group of dogs receives 10 mg of caffeine each, and the 3rd group
receives 50 mg of caffeine each. He will measure their activity levels by
recording how long each dog runs without stopping, after giving them the pills.
What is the dependent variable in this experiment?
A. The amount of dogs tested.
B. The dogs that receive water.
C. The amount of caffeine given.
D. The amount of activity.