n one study on the effect of niacin on cholesterol level, 100 subjects who acknowledged being longtime niacin takers had their cholesterol levels compared with those of 100 people who had never taken niacin. In a second study, 50 subjects were randomly chosen to receive niacin and 50 were chosen to receive a placebo.

Select one:

a.

The first study was a controlled experiment, while the second was an observational study.

b.

The first study was an observational study, while the second was a controlled experiment.

c.

Both studies were controlled experiments.

d.

Both studies were observational studies.