( Automobiles ( ( ( emit ( ( a lot ) ( of pollutants ) ) ) ( into ( ( ( the air ) , ) ( which ( can ( cause ( acid rain ) ) ) ) ) ) ) ; ) )
(ROOT (S (NP (NNS Automobiles)) (VP (VBP emit) (NP (NP (DT a) (NN lot)) (PP (IN of) (NP (NNS pollutants)))) (PP (IN into) (NP (NP (DT the) (NN air)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (MD can) (VP (VB cause) (NP (JJ acid) (NN rain))))))))) (: ;)))
Automobiles emit a lot of pollutants into the air, which can cause 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)))))) (. .)))