( ( Polycyclic ( Aromatic ( Hydrocarbons ( ( -LRB- ( PAHs -RRB- ) ) PAHs ) ) ) ) ( ( ( ( ( comprise ( ( one category ) ( of ( base/neutral ( and ( acid ( extractable compounds ) ) ) ) ) ) ) and ) are ) ( ( a group ) ( of ( chemicals ( that ( are ( formed ( during ( ( the burning ) ( of ( ( ( ( ( ( ( ( ( coal , ) oil ) , ) gas ) , ) wood ) , ) or ) ( other ( organic substance ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Polycyclic) (NNP Aromatic) (NNP Hydrocarbons) (PRN (-LRB- -LRB-) (NP (NNP PAHs)) (-RRB- -RRB-)) (NNP PAHs)) (VP (VP (VBP comprise) (NP (NP (CD one) (NN category)) (PP (IN of) (NP (NN base/neutral) (CC and) (JJ acid) (NN extractable) (NNS compounds))))) (CC and) (VP (VBP are)) (NP (NP (DT a) (NN group)) (PP (IN of) (NP (NP (NNS chemicals)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (VP (VBN formed) (PP (IN during) (NP (NP (DT the) (NN burning)) (PP (IN of) (NP (NP (NN coal)) (, ,) (NP (NN oil)) (, ,) (NP (NN gas)) (, ,) (NP (NN wood)) (, ,) (CC or) (NP (JJ other) (JJ organic) (NN substance)))))))))))))) (. .)))
Polycyclic Aromatic Hydrocarbons (PAHs) PAHs comprise one category of base/neutral and acid extractable compounds and are a group of chemicals that are formed during the burning of coal, oil, gas, wood, or other organic substance.
(ROOT (S (NP (NP (DT The) (NN action)) (PP (IN of) (S (VP (VBG burning) (NP (NP (DT a) (NN piece)) (PP (IN of) (NP (NN wood)))))))) (VP (VBZ forms) (NP (DT a) (JJ different) (NN chemical) (NN substance))) (. .)))