( ( ( The ( optimal ( frequency response ) ) ) ( of ( the ( human ear ) ) ) ) ( ( is ( 20Hz ( to ( 20,000 Hz ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ optimal) (NN frequency) (NN response)) (PP (IN of) (NP (DT the) (JJ human) (NN ear)))) (VP (VBZ is) (ADJP (JJ 20Hz) (PP (TO to) (NP (CD 20,000) (NNS Hz))))) (. .)))
The optimal frequency response of the human ear is 20Hz to 20,000Hz.
(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))))))))) (. .)))