Smoking elevates goblet cells and mucus, associating with but not causing lung disease

Steps:

• Group 1 (non-smokers, no disease) shows low goblet cell and mucus densities as baseline.
• Group 2 (smokers, no disease) has higher densities than group 1, linking smoking to increases.
• Group 3 (smokers with disease) shows even higher densities than group 2, associating disease with further elevation.
• Consistent correlation between goblet cells and mucus across groups indicates their production relationship.

Why C is correct:

• Data support statement 2 (goblet cells produce mucus, via density correlation) and 3 (smoking increases goblet cells, via group 1 vs. 2), but not 1 (smoking causes disease, as group 2 smokes without it), per observational study limits.

Why the others are wrong:

• A: Includes unsupported 1 (ignores group 2 lacking disease).
• B: Includes unsupported 1, excludes supported 3 (group 1 vs. 2 increase).
• D: Includes unsupported 1 despite evidence against direct causation.

Final answer: C