( Methane ( ( is ( ( a ( greenhouse gas ) ) ( that ( burns ( to ( form ( ( ( ( carbon dioxide ) ( -LRB- ( CO2 -RRB- ) ) ) and ) ( water vapor ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Methane)) (VP (VBZ is) (NP (NP (DT a) (NN greenhouse) (NN gas)) (SBAR (WHNP (WDT that)) (S (VP (VBZ burns) (S (VP (TO to) (VP (VB form) (NP (NP (NN carbon) (NN dioxide)) (PRN (-LRB- -LRB-) (NP (NNP CO2)) (-RRB- -RRB-)) (CC and) (NP (NN water) (NN vapor))))))))))) (. .)))
Methane is a greenhouse gas that burns to form carbon dioxide (CO2) and water vapor.
(ROOT (S (NP (NP (DT The) (NN combustion)) (PP (IN of) (NP (NN propane) (NN gas)))) (VP (VBZ produces) (NP (NP (NN carbon) (NN dioxide)) (CC and) (NP (NN water) (NN vapor)))) (. .)))