( It ( ( is ( responsible ( for ( ( equilibrating ( middle ( ear pressure ) ) ) ( to ( ( the pressure ) ( in ( the ( external environment ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (S (VP (VBG equilibrating) (NP (JJ middle) (NN ear) (NN pressure)) (PP (TO to) (NP (NP (DT the) (NN pressure)) (PP (IN in) (NP (DT the) (JJ external) (NN environment)))))))))) (. .)))
It is responsible for equilibrating middle ear pressure to the pressure in the external environment.
(ROOT (S (NP (DT The) (NNS ears)) (VP (VBP are) (NP (NP (DT an) (JJ external) (NN feature)) (PP (IN in) (NP (JJ human) (NNS beings))) (SBAR (S (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (NP (NN balance))))))))) (. .)))