Final answer:
The control in the experiment to determine if higher doses of hydroxychloroquine reduce patients' fever more effectively is b) The lower dose of hydroxychloroquine, which serves as a comparative baseline.
Step-by-step explanation:
In the described experiment, the control would be b) The lower dose of hydroxychloroquine. The control group is the group that receives either a standard treatment or placebo, against which the experimental group is compared. It is important to have a control group to establish a baseline for what happens without the experimental treatment. In this case, patients receiving the lower dose serve as a baseline to assess the efficacy of the higher dose. The lower dose is not intended to cause change, but to serve as a comparative point for understanding whether the higher doses of hydroxychloroquine are more effective.