( ( ( ( Hydrogen gas ) and ) ( oxygen gas ) ) ( ( combine ( to ( form water ) ) ) . ) )
(ROOT (S (NP (NP (NN Hydrogen) (NN gas)) (CC and) (NP (NN oxygen) (NN gas))) (VP (VBP combine) (S (VP (TO to) (VP (VB form) (NP (NN water)))))) (. .)))
Hydrogen gas and oxygen gas combine to form water.
(ROOT (S (NP (NNP Hydrogen)) (VP (VBZ is) (PP (IN in) (NP (NP (NN gas) (NN form)) (PP (IN at) (NP (NN room) (NN temperature)))))) (. .)))