Don't Guess.

Give Reason for your Answer.

A study was done to compare the lung capacity of miners to the lung capacity of farmers. The researcher studied 200 workers of each type. Other factors that might affect lung capacity are smoking habits and exercise habits. The smoking habits of the two worker types are similar, but the miners generally exercise less than the farmers. Which of the following factors could confound the statistics in this study? O A. Occupation O B. Lung capacity O C. Exercise O D. Smoker or non-smoker