A researcher is studying the effects of different artificial sweeteners on rats. Sixty full-grown rats were divided into six groups of ten. The first group received no artificial sweeteners. The rest of the groups received various artificial sweeteners. Each group of rats were treated at the same points of the day for four months. The rats were than biologically analyzed after each day and results were analyzed at the end of the experiment. What was the control in the experiment?

A) The size of the rats.
B) The length of the experiment.
C) The group of rats that received artificial sweetener.
Eliminate
D) The group of rats that received no artificial sweetener.