( ( ( ( ( The ( ( most common ) form ) ) , ) ( nitrogen narcosis ) ) , ) ( ( is ( caused ( by ( ( breathing ( compressed air ) ) ( at depth ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (ADJP (RBS most) (JJ common)) (NN form)) (, ,) (NP (NN nitrogen) (NNS narcosis)) (, ,)) (VP (VBZ is) (VP (VBN caused) (PP (IN by) (S (VP (VBG breathing) (NP (JJ compressed) (NN air)) (PP (IN at) (NP (NN depth)))))))) (. .)))
The most common form, nitrogen narcosis, is caused by breathing compressed air at depth.
(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)))))))) (. .)))