( ( Auto emissions ) ( ( are ( ( the ( primary cause ) ) ( of ( air pollution ) ) ) ) . ) )
(ROOT (S (NP (NN Auto) (NNS emissions)) (VP (VBP are) (NP (NP (DT the) (JJ primary) (NN cause)) (PP (IN of) (NP (NN air) (NN pollution))))) (. .)))
Auto emissions are the primary cause of air pollution.
(ROOT (S (NP (JJ Primary) (NNS pollutants)) (VP (VBP enter) (NP (DT the) (NN air)) (ADVP (RB directly))) (. .)))