( It ( ( occurs ( combined ( with ( ( other chemicals ) ( such ( as ( sulfur ( or ( ( carbon and ) oxygen ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ occurs) (PP (VBN combined) (PP (IN with) (NP (NP (JJ other) (NNS chemicals)) (PP (JJ such) (IN as) (NP (NN sulfur) (CC or) (NN carbon) (CC and) (NN oxygen))))))) (. .)))
It occurs combined with other chemicals such as sulfur or carbon and oxygen.
(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))))))) (. .)))