Question

NEED HELP!!!!!! Which situation is an example of an observational study? A. Collecting the cholesterol readings of a group of people in a certain age group in a small town B. Testing the effectiveness of a new hair product by allowing one group to use it and comparing results against a group that doesn’t use it C. Finding out the number of monthly burglaries of a residential neighborhood for a statistical study for the police D. Calling a sample of registered voters before an election to find out what issues concern them most