Denise smoked a lot when she was younger. She is now being treated for lung cancer. She is the only person in her family who has lung cancer. Which of these was the most likely type of direct cause of Denise’s cancer?

Denise’s heavy smoking is an environmental exposure that can directly damage lung cells and cause cancer. Because she is the only family member with lung cancer, the question gives less reason to suspect an inherited genetic cause. The best choice is environmental.

AI-written and checked against the verified answer.