A 51-year-old man has been diagnosed with chronic bronchitis after a long history of recurrent ...

A 51-year-old man has been diagnosed with chronic bronchitis after a long history of recurrent coughing. Which of the man's following statements demonstrates a sound understanding of his new diagnosis?
 
  A) If I had quit smoking earlier than I did, I think I could have avoided getting bronchitis.
  B) I'm pretty sure that I first caught bronchitis from the person who has the cubicle next to mine at work.
  C) I read on the Internet that I might have got bronchitis because I was born with an enzyme deficiency.
  D) I think that I probably could have prevented this if I had got in the habit of exercising more when I was younger.