In a small study, 12 women with cervical cancer (cancer of the cervix) and 12 women with no apparent cervical cancer were contacted and asked whether they had ever used the hormone estrogen as a drug. Each woman with cancer was matched by age, race, and weight with a woman without the disease. This is an example of:
a) A randomized controlled trial
b)A prospective cohort study
c) A case-control study
d) A retrospective cohort study