( ( As ( they swim ) ) ( , ( they ( ( breathe ( ( air bubbles ) ( trapped ( beneath ( the ice ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (NP (PRP they)) (VP (VBP swim)))) (, ,) (NP (PRP they)) (VP (VB breathe) (NP (NP (NN air) (NNS bubbles)) (VP (VBN trapped) (PP (IN beneath) (NP (DT the) (NN ice)))))) (. .)))
As they swim, they breathe air bubbles trapped beneath the ice.
(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)))))))) (. .)))