( ( A diver ) ( ( is ( ( ( using ( a ( NITROX mixture ) ) ) ( -LRB- ( ( oxygen ( ( enriched air ) ( to ( ( reduce ( risk ( of ( decompression ( ( illness and ) increase ) ) ) ) ) ( bottom time ) ) ) ) ) -RRB- ) ) ) ( to ( breath underwater ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN diver)) (VP (VBZ is) (VP (VBG using) (NP (DT a) (NNP NITROX) (NN mixture)) (PRN (-LRB- -LRB-) (S (NP (NN oxygen)) (VP (VBD enriched) (NP (NN air)) (S (VP (TO to) (VP (VB reduce) (NP (NP (NN risk)) (PP (IN of) (NP (NN decompression) (NN illness) (CC and) (NN increase)))) (NP (JJ bottom) (NN time))))))) (-RRB- -RRB-)) (PP (TO to) (NP (NN breath) (NNS underwater))))) (. .)))
A diver is using a NITROX mixture (oxygen enriched air to reduce risk of decompression illness and increase bottom time) to breath underwater.
(ROOT (S (NP (DT An) (JJ underwater) (NN spider)) (VP (VBZ uses) (NP (JJ shiny) (NN air) (NN bubble) (S (VP (TO to) (VP (VP (VB breathe)) (CC and) (VP (VB keep) (ADJP (JJ alive)))))))) (. .)))