( It ( ( is ( ( fluid , ) ( ( composed mostly ) ( of ( ( hydrogen and ) helium ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (NP (NP (NN fluid)) (, ,) (VP (VBN composed) (ADVP (RB mostly)) (PP (IN of) (NP (NN hydrogen) (CC and) (NN helium)))))) (. .)))
It is fluid, composed mostly of hydrogen and helium.
(ROOT (S (NP (NNP Saturn)) (VP (VBZ is) (VP (VBN made) (ADVP (RB mostly)) (PP (IN of) (NP (NN helium) (CC and) (NN hydrogen))))) (. .)))