D and C

@Kanyin, Happy to help. Let's take a look at (D) and (C). (D) says, "presumes, without providing justification, that anyone who does not have lung disease is in good health" It's true that the conclusion is about how exercise can help lead to a health benefit, but the problem with (D) is that the argument in the stimulus never makes the conclusion that anyone who doesn't have lung disease is in good health; rather, the argument states that they receive a benefit to their health. Thus, (D) is out. (C) says, "concludes merely from the fact that two things are correlated that one causes the other" (C) is great because, as noted in the stimulus, there's a strong correlation between exercise and a reduced risk of lung disease. The argument then makes the conclusion that exercise is the cause of this health benefit, which is mistaking correlation for causation. This is just what (C) says, so it's the correct answer. Does this make sense? Let us know if you have any other questions!