In one study on the effect of tea tree oil on acne, 65 subjects were chosen randomly to use tea tree oil and 65 were chosen to use a placebo. In a second study, 165 subjects who acknowledged being long-time tea tree oil users had their acne compared with those of 165 people who had never used tea tree oil. Identify the types of studies performed. (4 points) A. Both studies were controlled experiments.
B. Both studies were observational studies.
C. Each study was part controlled experiment and part observational study.
D. The first study was an observational study whereas the second was a controlled experiment.
E. The first study was a controlled experiment whereas the second was an observational study.