Answer:
The 1st group of dogs
Explanation:
The control group in an experiment is the group that does not receive treatment, or the one that is not subjected to the independent variable. A control group is used to determine that no other influence or other outside variables would cause the change in the subjects.
For example, if the dogs in the control group would experience the same changes that the dogs that were tested (the ones that got caffeine), then that would mean that it was not the caffeine that elicited the change in the subject.