Which Statement Best Describes Case-Control Studies

Which statement best describes case-control studies?

A) They are in-depth studies of a single case.
B) They are studies in which control is exerted over the treatment individuals get.
C) They are studies in which a risk exposure is identified and the persons are followed to see how the disease or condition develops.
D) They are studies in which persons with and without a rare outcome are studied and then there is a backward look for risk exposures.