( ( Indoor ( air pollutants ) ) ( ( can ( be ( classified ( in ( different ways ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Indoor) (NN air) (NNS pollutants)) (VP (MD can) (VP (VB be) (VP (VBN classified) (PP (IN in) (NP (JJ different) (NNS ways)))))) (. .)))
Indoor air pollutants can be classified in different ways.
(ROOT (S (NP (NP (NNP Ash)) (SBAR (WHNP (WDT that)) (S (VP (VBZ enters) (NP (DT the) (NN air)) (PP (ADVP (RB naturally)) (IN as) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (DT a) (NN volcano) (NN eruption))))))))) (VP (VBZ is) (VP (VBN classified) (PP (IN as) (NP (DT a) (JJ primary) (NN pollutant))))) (. .)))