( ( ( ( Volatile ( air pollutants ) ) and ) smoking ) ( ( are ( ( the ( primary causes ) ) ( of bronchitis ) ) ) . ) )
(ROOT (S (NP (NP (JJ Volatile) (NN air) (NNS pollutants)) (CC and) (NP (NN smoking))) (VP (VBP are) (NP (NP (DT the) (JJ primary) (NNS causes)) (PP (IN of) (NP (NNS bronchitis))))) (. .)))
Volatile air pollutants and smoking are the primary causes of bronchitis.
(ROOT (S (NP (JJ Primary) (NNS pollutants)) (VP (VBP enter) (NP (DT the) (NN air)) (ADVP (RB directly))) (. .)))