Some Environmental Scientists Have Interviewed Residents in a Community Where

Some environmental scientists have interviewed residents in a community where there are many fuel processing plants. It seems that there is a high cancer rate in the area. Which of the following will provide the scientists with the data they need for 100% certain results that the cancer rates are directly correlated to the fuel processing plants?

A) Surveys of residents affected by cancer and how close they live to the processing plants
B) Blood tests of those with cancer who live near the processing plants
C) Blood tests of people before they move near the plants and then a few years later after living near the plants
D) All of the above
E) None of the above