( Sulfur ( trioxide ... ) )
(ROOT (NP (JJ Sulfur) (NN trioxide) (: ...)))
Sulfur trioxide....................................
(ROOT (S (NP (NNP Sulfur)) (VP (MD can) (VP (VB combine) (PP (IN with) (NP (NN oxygen))) (S (VP (TO to) (VP (VB produce) (NP (NN sulfur) (NN trioxide))))))) (. .)))