( ( ( ( ( Carpool or ) ride ) ( the bus ) ) ( to ( prevent ( ( ( air pollution ) , ) ( which ( causes ( acid rain ) ) ) ) ) ) ) . )
(ROOT (S (VP (VB Carpool) (CC or) (VB ride) (NP (DT the) (NN bus)) (S (VP (TO to) (VP (VB prevent) (NP (NP (NN air) (NN pollution)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ causes) (NP (JJ acid) (NN rain)))))))))) (. .)))
Carpool or ride the bus to prevent air pollution, which causes 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)))))) (. .)))