In a case-control study of a suspected association between breast cancer and the contraceptive pill.All of the following are true statements except:

• A. The control should come from a population that has the same potential for breast cancer as the cases.
• B. The control should exclude woman known to be taking the pill at the time of the survey.
• C. All the controls need to be healthy
• D. The attributable risk of breast cancer resulting from the pill may be directly measured