A. Interviewing college students to find what percentage expects a job immediately after graduation
O B. Collecting the cholesterol readings of a group of elderly people in
a small town
O C. Testing the effectiveness of a mouthwash by allowing one group
to use it and comparing the results with those of a group that
doesn't use it
O D. Testing the effectiveness of a hair product by allowing one group
to use it and comparing results against a control group