Critical Reasoning (CR) | Re: In 1990, nearly 80% of people in the United States reported

Hmm I was torn between B and D, and decided to go with B.

D sounds ok, but only some of the newly diagnosed cancer happened to people who already had some other form of cancer.
B is better per network theory - high frequency in densely populated area means there already were a lot of people who knew someone with cancer.

Best CR decision I've made today so far XD

---