Determine whether the study is an observational study or an experiment.
A medical researcher obtains a sample of adults suffering from diabetes. She randomly assigns 89 people to a treatment group and 89 to a placebo group. The treatment group receives a medication over a period of three months and the placebo group receives a placebo over the same time frame. At the end of three months the patients' symptoms are evaluated.
A) experiment
B) observational study