( ( Air pollution ) ( ( can ( result ( in ( acid rain ) ) ) ) . ) )
(ROOT (S (NP (NNP Air) (NN pollution)) (VP (MD can) (VP (VB result) (PP (IN in) (NP (JJ acid) (NN rain))))) (. .)))
Air pollution can result in acid rain.
(ROOT (S (NP (JJ Acid) (NN rain)) (VP (MD may) (VP (VB be) (VP (VBN caused) (PP (IN by) (NP (NN air) (NN pollution)))))) (. .)))