A Researcher Assesses the Smoking and Drinking Habits of a Group

Multiple Choice

A researcher assesses the smoking and drinking habits of a group of retired ex-coal miners, and also assesses their grip strength. The researcher finds that the miners who smoke and drink more have higher strength. What can they conclude:

A) Smoking and drinking make you stronger.
B) People who exercise more smoke and drink more.
C) This can't be true.
D) There is probably a third variable that we have not accounted for.