( ( ( ( ( Breathing ( ( gas mixtures ) ( other ( than ( air underwater ) ) ) ) ) and ) especially ) ( ( using ( rebreather devices ) ) underwater ) ) ( , ( ( are ( activities ( which ( require ( additional ( specialized training ) ) ) ) ) ) . ) ) )
(ROOT (S (S (VP (VP (VBG Breathing) (NP (NP (NN gas) (NNS mixtures)) (PP (JJ other) (IN than) (NP (NN air) (NNS underwater))))) (CC and) (ADVP (RB especially)) (VP (VBG using) (NP (NN rebreather) (NNS devices)) (ADVP (RB underwater))))) (, ,) (VP (VBP are) (NP (NP (NNS activities)) (SBAR (WHNP (WDT which)) (S (VP (VBP require) (NP (JJ additional) (JJ specialized) (NN training))))))) (. .)))
Breathing gas mixtures other than air underwater and especially using rebreather devices underwater, are activities which require additional specialized training.
(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)))))))) (. .)))