At a local health club, a researcher samples 75 people whose primary exercise is cardiovascular and 75 people whose primary exercise is strength training. The researchers objective is to assess the effect of type of exercise on cholesterol. Each subject reported to a clinic to have his or her cholesterol measured. The subjects were unaware of the purpose of the study, and the technician measuring the cholesterol was not aware of the subjects' type of exercise. This is
A. an observational study
B. an experiment, but not a double-blind experiment.
C. a double-blind experiment.
D. a matched pairs experiment.