A March 2010 headline from esciencenews.com said, Exposure to tobacco smoke in childhood home associated with early

Question:

A March 2010 headline from esciencenews.com said, "Exposure to tobacco smoke in childhood home associated with early emphysema in adulthood."
a. Is this headline more likely to refer to a controlled experiment or to an observational study? Explain.
b. Suggest a potential factor that might explain the association between childhood exposure to smoking and early emphysema.