Answer:
The amount of activity
Explanation:
In an experiment, the independent variable is the variable that the scientist/investigator purposely changes or manipulates, which isn't changed by other variables in the experiment (in this case, the amount of caffeine). On the other hand, the dependent variable is the variable that is being measured or tested during the experimental procedure (this variable is 'dependent' on the independent variable). Finally, the control group is defined as the group of individuals/subjects who do not receive the experimental treatment (in this case, the dogs that receive water).