( ( ( an ( external stimulus ) ) ( to ( the ear ) ) ) ( ( can ( produce ( only ( an ( auditory response ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT an) (JJ external) (NN stimulus)) (PP (TO to) (NP (DT the) (NN ear)))) (VP (MD can) (VP (VB produce) (NP (RB only) (DT an) (JJ auditory) (NN response)))) (. .)))
an external stimulus to the ear can produce only an auditory response.
(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))))))))) (. .)))