( ( List ( ( three barriers ) ( oxygen ( must ( ( ( ( ( cross ( from ( the alveolus ) ) ) ( into ( the capillaries ) ) ) , ) and ) ( explain ( ( the advantage ) ( of ( having ( millions ( of ( alveoli ( in ( the lungs ) ) ) ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (VP (VB List) (NP (NP (CD three) (NNS barriers)) (SBAR (S (NP (NN oxygen)) (VP (MD must) (VP (VP (VB cross) (PP (IN from) (NP (DT the) (NNS alveolus))) (PP (IN into) (NP (DT the) (NNS capillaries)))) (, ,) (CC and) (VP (VB explain) (NP (NP (DT the) (NN advantage)) (PP (IN of) (S (VP (VBG having) (NP (NP (NNS millions)) (PP (IN of) (NP (NP (NNS alveoli)) (PP (IN in) (NP (DT the) (NNS lungs))))))))))))))))) (. .)))
List three barriers oxygen must cross from the alveolus into the capillaries, and explain the advantage of having millions of alveoli in the lungs.
(ROOT (S (NP (NP (DT The) (NNS lungs)) (PP (IN of) (NP (NNS mammals)))) (VP (VBP are) (ADJP (JJ unique) (PP (IN in) (S (VP (VBG having) (NP (NNS alveoli))))))) (. .)))