Hello!
The control in an experiment is the part of an experiment which you are basing yours off of, for example, if an experiment was how much faster a flower would grow with a new fertilizer in the soil, the control would be the growth rate of the flowers without any fertilizer.
In this case, the thing being experimented with is the new medication. So the control would be the people without the medicine, or in this case, the placebo (as it essentially has the same effect.)
Therefore, your answer would be C.
Hope this helped!