Answer:
A. The dogs that receive water.
Step-by-step explanation:
In an experiment, we have the control group and the experimental groups. As opposed to the experimental group, the CONTROL GROUP is that group that does not receive any of the experimental treatment (independent variable).
According to this question, a student is conducting an experiment to test the effect of caffeine on dogs. The student uses 3 groups of dogs and gives each group the following respectively: plain water, 10mg caffeine, 50mg caffeine. The control group, which is the group that doesn't receive the caffeine (test material) is the dogs that receive water (GROUP 1).