( ( Most ( commonly used ) ) ( ( are ( Helium ( , ( Argon ( , ( ( Nitrogen and ) Hydrogen ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (JJS Most)) (ADJP (RB commonly) (VBN used))) (VP (VBP are) (NP (NNP Helium) (, ,) (NNP Argon) (, ,) (NNP Nitrogen) (CC and) (NNP Hydrogen))) (. .)))
Most commonly used are Helium, Argon, Nitrogen and Hydrogen.
(ROOT (S (NP (NNP Nitrogen) (, ,) (NNP oxygen) (CC and) (NNP argon)) (VP (VBP are) (NP (NP (DT the) (CD three) (JJS most) (JJ common) (NNS elements)) (PP (IN in) (NP (NP (DT the) (NN air)) (SBAR (S (NP (PRP we)) (VP (VB breathe)))))))) (. .)))