5. A medical researcher wants to determine whether exercising can lower blood pressure. At a health fair, he measures the blood pressure of 100 individuals, and interviews them about their exercise habits. He divides the individuals into two categories: those whose typical level of exercise is low, and those whose level of exercise is high. a. Is this a controlled experiment or an observational study? b. The subjects in the low exercise group had considerably higher blood pressure, on the average, than subjects in the high exercise group. The researcher concludes that exercise decreases blood pressure. Is this conclusion well-justified? Explain.