When the body absorbs nicotine, it converts it into cotinine. Experiments have ruled out coincidence as an explanation for a correlation between exposure to second-hand smoke and cotinine in the body. The only possible explanations for that correlation are that the exposure causes cotinine or that there is some other underlying cause.

For Exercises 5–8, decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly; not all of these statements have definitive answers, so your explanation is more important than your chosen answer.